[This briefing has ended. Read the latest updates on the coronavirus epidemic here.]

The count: 28 countries, with a spike in South Korea.

South Korea reported 123 new coronavirus cases on Sunday, bringing its total to 556, and reported a fourth death. The news added to concerns that another Asian country was losing control of the disease and that the window to avert a pandemic was closing.

As of Saturday, the virus had spread to 28 countries. Some 1,500 cases had been confirmed outside China; multiple infections in the United States, Italy, Iran and the United Arab Emirates; and one in Egypt, the first to be confirmed on the African continent. The highest death toll outside of China is in Iran, with six as of Saturday.

Early Sunday, China, where the virus emerged, raised its numbers to 76,936 confirmed cases and 2,442 deaths.

Panic was spreading in Israel on the news that nine South Koreans who had spent a week visiting often-crowded religious sites as part of a Roman Catholic tour group had tested positive upon returning home.

Many African countries are bracing for the disease. The World Health Organization has identified 13 as priorities because of their direct links to China or their high volume of travel to it.

South Korea’s fourth-largest city is in a state of emergency.

With hundreds of infections having been confirmed in South Korea in just a few days, Prime Minister Chung Sye-kyun called the situation “grave.”

“We will deal sternly with any acts that interfere with the government’s quarantine efforts and add to anxiety among the people,” Mr. Chung said in a nationally televised statement on Saturday. He urged citizens not to hoard facial masks or other hygiene products.

More than half of the country’s 556 cases are among members of a secretive religious sect, the Shincheonji Church of Jesus, and their relatives or contacts. Between Daegu, the country’s fourth largest city, and a nearby province where the sect’s members often do volunteer work, 465 people have tested positive.

More than 1,250 members of the sect have reported potential symptoms, and officials are still trying to locate hundreds of members so they can be screened.

The neighborhood around the sect’s church in Daegu has turned into a ghost town. Banks, coffee shops, restaurants and convenience stores have all shut down.

Across the city of 2.4 million, department stores, shopping alleys and outdoor marketplaces are drained of shoppers.

The only places more crowded than usual are government-run health centers, where citizens lined up to find out whether they were infected.

In Busan, South Korea’s second largest city, public libraries, a horse racetrack and facilities for senior citizens closed when the city reported its first coronavirus case on Friday.

Many churches have shuttered, instead offering prayer services online. Others stayed open, but skipped hymns or “Amens” to limit congregants’ exposure.

The national news agency Yonhap reported people emptying shelves of rice, instant noodle, eggs and other essential food items in some supermarkets in Chuncheon and Ulsan, as both cities reported their first cases on Saturday.

Samsung, the world’s smartphone maker, shut down a factory about an hour north of Cheongdo after a worker tested positive. The factory is expected to resume operations on Monday morning, Samsung said. But the floor of the factory where the patient has worked will be closed until Tuesday morning, it said.

President Trump was furious over the repatriations of infected Americans.

The news that 14 American citizens from the Diamond Princess who had tested positive for the coronavirus were being flown to the United States this week surprised and infuriated President Trump, two senior American officials said.

The Washington Post first reported Mr. Trump’s anger on Friday. The president is a self-declared “germophobe.”

Mr. Trump conveyed his anger to Alex M. Azar II, the health and human services secretary overseeing the White House interagency task force on the coronavirus, and other top officials. The task force’s top State Department official is Stephen E. Biegun, the deputy secretary of state.

One official said that Mr. Trump views keeping infected people from entering the country as critical to keeping the country safe and that the president wants to be seen as managing a proper response.

The decision to fly back the infected passengers was made over the objections of officials at the Centers for Disease Control.

On Monday, after two planes carrying more than 300 evacuated passengers had landed at military bases in Texas and California, William Walters, a top medical official at the State Department, told reporters that the decision to keep the 14 infected Americans in the group had been made by the State Department in consultation with Robert Kadlec, an assistant secretary at the Department of Health and Human Services.

Dr. Walters said that the evacuation had already begun when Japanese officials informed their American counterparts of the laboratory test results. Dr. Walters said that he had spoken with Dr. Kadlec to go over the options after learning of the test results.

Since the passengers returned, Japanese officials have informed American officials that several more of them had also tested positive for coronavirus.

On Friday, American officials said at least 34 people inside the United States have the virus — 18 of them from the Diamond Princess. All of the 34 cases have been linked to overseas travel. There has been no sign yet of the virus spreading among communities in the United States.

The W.H.O. heads to Wuhan, and says it fears for Africa.

A team of experts from the World Health Organization were traveling on Saturday to the Chinese city of Wuhan, the center of the coronavirus epidemic, the agency’s director general, Tedros Adhanom Ghebreyesus, said.

Health professionals from the U.N. agency have worked on the outbreak in three Chinese provinces — Beijing, Sichuan and Guangdong — but had not yet been to the city at its heart.

Dr. Tedros confirmed the trip during an address on Saturday morning to African officials from Geneva, where he spoke of the virus’s increasing global spread and urged them to prepare for possible cases on their continent.

“We have to take advantage of the window of opportunity we have, to attack the virus outbreak with a sense of urgency,” Dr. Tedros told the leaders, who had gathered for an emergency meeting on the response to the coronavirus in the continent.

With only one confirmed case on the continent, Africa has so far been mostly spared, but health officials have warned that the spread could be deadly in countries with already-strained health systems. The W.H.O. has provided online training on the coronavirus to 11,000 African health workers.

China and Africa have become intertwined in the last two decades as China has expanded its political, economic, and military ties to Africa, funding large infrastructure projects and pledging tens of billions of dollars in investments and loans.

Now, Africa has large numbers of Chinese workers and more than 81,000 Africans were studying in mainland China in 2018. About 4,600 African citizens and students were living in Wuhan.

While some African countries, including Morocco, Mauritius and Egypt, have evacuated their citizens from China, Kenya has not. On Friday, the Kenyan government explained its rationale on Twitter, saying “the safest place for the students to be is Wuhan.”

Israel bars South Korean tourists.

Nine South Korean tourists who spent a week visiting some of Israel’s most popular religious sites have tested positive for the coronavirus after returning home. Within hours, Israel began closing the country to South Korean travelers altogether.

Korean passengers flying on a Korean Air flight scheduled to land at Ben Gurion Airport at 7:30 p.m. Saturday would be barred entry into the country, Ynet reported late Saturday afternoon. Kan radio said that, on Sunday, the government would discuss whether to allow the other South-Korea-to-Tel Aviv flights to continue.

Israel’s health ministry ordered the immediate suspension of all tours by South Korean tourists who are currently in Israel, according to Kan radio. Health officials were working with the tourism ministry and travel agencies to book flights back to South Korea for the 1,700 South Korea tourists in Israel.

Israel suspended all flights from China on Jan. 30 in response to the outbreak of coronavirus.

The nine South Korean tourists were among a Roman Catholic tour group of 77 people, Haaretz reported. The health ministry said the pilgrims visited Israel from Feb. 8 to Feb. 15, touring Christian sites and other attractions in Netanya, Caesaria, Nazareth, the Sea of Galilee, the Dead Sea, Beersheva, Hebron and Jerusalem.

Among the often-crowded sites the group visited were the Cave of the Patriarchs in Hebron and the Church of the Holy Sepulcher in Jerusalem.

The health ministry said it was conducting an epidemiological investigation to identify anyone who came in contact with the group.

Twenty Israel Nature and Parks Authority employees and two Dead Sea hotel housekeeping employees who were in contact with the South Korea tourists have already been placed in quarantine, according to local reports.

Russian disinformation blames U.S. for coronavirus.

State Department officials say that thousands of Russia-linked social media accounts are spreading disinformation about the coronavirus, including a conspiracy theory that the United States is behind the Covid-19 outbreak.

American monitors identified the campaign in mid-January. Agence-France Presse first reported on the assessment on Saturday.

“Russia’s intent is to sow discord and undermine U.S. institutions and alliances from within, including through covert and coercive malign influence campaigns,” said Philip Reeker, the acting assistant secretary of state for Europe and Eurasia.

“By spreading disinformation about coronavirus, Russian malign actors are once again choosing to threaten public safety by distracting from the global health response.”

The effort was described as being carried out by several thousand Russia-linked accounts on Instagram, Facebook and Twitter, which post similar messages at similar times in English, Spanish, French, German and Italian.

Fringe theories of uncertain origin have accused China of engineering the virus, including suggesting that it is an escaped bioweapon.

Misinformation about the virus — whether shared purposefully or unwittingly — is so rife that the World Health Organization has called it an “infodemic.” The W.H.O. has been working with big tech companies to try to quell the flood of rumors and falsehoods.

Iran’s death toll from the virus reaches six, the highest outside China.

Iran, which insisted as recently as Tuesday that it had no coronavirus cases, confirmed 28 cases and six deaths on Saturday, according to Iranian state media, making it the country with the highest death toll outside of China, where the number climbed to 2,345 on Saturday.

On Saturday, Dr. Tedros Adhanom Ghebreyesus, the World Health Organization’s director, said the organization was “especially concerned about the increase in cases in the Islamic Republic of Iran.”

Iran was the first country in the Middle East to declare deaths related to the virus. The head of public relations at the country’s health ministry, Kianush Jahanpur, wrote in a tweet that most of the infections came from Qom, 80 miles south of the capital, Tehran. Officials also confirmed cases in Tehran, and in the northern city of Rasht.

The number of deaths suggest the virus is being transmitted far more widely than Iranian officials have acknowledged. Infectious health experts note that, if, as Chinese doctors have reported, the virus kills about 2 percent of known victims, multiplying the number of deaths by 50 offers a rough case estimate. On that logic, Iran could have 300 cases.

Already, cases of travelers from Iran testing positive for the virus have turned up in Canada and Lebanon, and on Saturday, the United Arab Emirates said two Iranian travelers had the virus, raising that country’s total cases to 13.

State media in Iran reported that universities and institutions of higher education were closed for a week in 10 provinces and schools were closed for three days in Tehran because of the virus. Seminaries in Qom were also closed.

Concerts, movies and other cultural events were canceled across the country for a week, state media said. And spectators were barred from soccer games countrywide.

Kuwait Airways announced Saturday that it would evacuate more than 700 Kuwaiti nationals from Mashhad, Iran.

As Iran holds parliamentary elections this weekend, many voters in Qom lined up in front of voting stations wearing masks, according to videos from Iranian news agencies.

Conflicting news reports emerged on Saturday about the mayor of a district of Tehran, who was said to have been hospitalized with coronavirus symptoms on Friday. But the semiofficial news agency Fars later denied that the mayor, Morteza Rahmanzadeh, had been hospitalized, saying he was in good health.

The C.D.C. lifts restrictions on Westerdam cruise ship passengers.

The U.S. Centers for Disease Control and Prevention has advised American passengers of the Westerdam cruise ship that they do not need to self-quarantine and are no longer subject to travel restrictions after their lives were upended when a fellow passenger was found to have the coronavirus.

No other infections have been found among passengers on the Westerdam, a C.D.C. spokesman said on Saturday, adding that the organization had sent an advisory to state and local health departments this past week.

An American woman, 83, who had disembarked from the Westerdam in Cambodia along with more than 2,000 other passengers and crew members, had tested positive for the coronavirus after arriving at the airport in Kuala Lumpur, Malaysia, on a subsequent layover, Malaysian officials said on Feb. 15. Only a small number of passengers had been tested before they were allowed to disembark.

The American passenger’s diagnosis, which Malaysian officials said was confirmed in a second test, had raised fears that another vector of transmission was going global. Cambodia has called the Malaysian diagnosis flawed.

That no other Westerdam passengers have become ill is not proof in itself that the American woman’s diagnosis was flawed, said Dr. William Schaffner, an infectious disease specialist at Vanderbilt University Medical Center.

But Dr. Schaffner said the C.D.C. has been “very meticulous about implementing a containment policy in the U.S. and has been assiduous about finding and monitoring people who’ve had contact or previous exposure.”

On Saturday, the Malaysian health director general, Noor Hisham Abdullah, said that the American passenger was now clear of the coronavirus and was being monitored in the hospital with a “slight cough,” after an antiretroviral treatment.

People who have recovered from the infection will test negative as their bodies clear the virus.

Cambodia’s prime minister, Hun Sen, who had personally welcomed the ship’s passengers after they had been turned away from several other ports, called Malaysia’s diagnosis into question again on Saturday. The woman never had coronavirus at all, he said.

Mr. Hun Sen is a close ally of China and his claims have cast doubts on the seriousness of the coronavirus outbreak.

Japan admits releasing some untested cruise ship passengers by mistake.

Just days after releasing nearly 1,000 passengers from the cruise ship quarantined for two weeks in the port of Yokohama that has been a coronavirus hot spot, Japan’s health minister admitted that 23 passengers had been mistakenly cleared to leave without taking a valid recent test.

In a news briefing on Saturday night, the health minister, Katsunobu Kato, apologized for the error that allowed the passengers, who had not been tested since before the ship went into lockdown on Feb. 5, to leave the Diamond Princess.

The Japanese Health Ministry said it had tested them and checked for symptoms, and certified that they posed “no risk of infection.”

Mr. Kato said that all 23 mistakenly cleared passengers had boarded some form of public transportation after disembarking. He said none of them had reported any symptoms so far and 20 had already agreed to be retested, with three negative tests so far.

Although several governments that evacuated citizens from the ship — including those in the United States, Australia, Hong Kong and South Korea — confined them for an additional 14 days at home, Japan said that passengers who had tested negative for coronavirus and showed no symptoms could leave starting this week.

On the subject of the passengers released untested, Mr. Kato said that public health officers who had been conducting the tests missed the 23 passengers as they went door to door.

“While they made their multiple rounds to take samples, some passengers left their rooms to go outside and do exercise or something,” he said, “so they were unavailable.”

A total of 634 people tested positive on board the cruise ship, and two passengers infected with the coronavirus have died.

Reporting and research were contributed by Hannah Beech, Liz Alderman, Vivian Wang, Choe Sang-Hun, Elian Peltier, Donald G. McNeil Jr., Farnaz Fassihi, Amy Harmon, Steven Lee Myers, Elaine Yu, Marc Santora, Matt Philips, Niraj Chokshi, Amie Tsang, Keith Bradsher, Amber Wang, Yiwei Wang, Ed Wong, David Halbfinger and Derrick Bryson Taylor.