KABUL — With the number of coronavirus cases in Pakistan soaring to more than 700 in the past few days, officials there have banned all international flights and have requested that security forces help institute a full lockdown in Sindh province, where a majority of cases have been reported. A third death from the virus was reported Friday.

Most of those found to be infected are Shiite pilgrims from Sindh who returned from visiting shrines in neighboring Iran, where the virus has already killed more than 1,500. Most reentered Pakistan via a single border crossing in Baluchistan province. A similar problem is affecting next-door Afghanistan, where tens of thousands of refugees have recently flooded back from Iran.

Pakistani Prime Minister Imran Khan, facing public panic, has stopped short of declaring a nationwide lockdown but has asked all citizens to self-quarantine for two weeks. This past week, Khan came under strong criticism after playing down the threat in a nationwide address. He said that people should not “run to hospitals” to get tested and that 90 percent of those testing positive would “recover easily.”

On Friday, with several hundred new cases reported, Khan told a group of TV anchors that he hoped the coming of hot and dry weather would mitigate the outbreak. He urged people to stay at home but remain calm, saying that “panicking is more dangerous for us than coronavirus.” He said he was still reluctant to impose a nationwide lockdown because it would harm the working poor.

“We don’t want to try and save people from corona but they end up dying due to hunger and poverty,” Khan said. Pakistan, a Muslim-majority country of 210 million, has a high poverty rate, with about one-quarter of the populace earning less than $2 per day.

But in Sindh, a vast and impoverished region of close to 50 million, officials decided to impose a total lockdown beginning Sunday night. Chief Minister Murad Ali Shah was in discussions with army and police officials Sunday night and was expected to formally enlist their help to ensure public compliance with the lockdown.

“Time for some tough decisions,” Murtaza Wahab, the minister’s spokesman, said in a tweet early Sunday. He said security forces would probably be asked to “ensure full implementation” of the decision to keep people in their homes, while grocery stores and pharmacies will remain open.

But the leader of the Pakistan People’s Party, which is based in Sindh, said the country needs to impose a nationwide lockdown to prevent the virus from spreading further. In a tweet Saturday, Bilawal Bhutto said the decision had been delayed for too long.

“We do need to learn from the experiences of other countries,” he said in the tweet, noting that the unchecked virus could “overwhelm” the public health system. “While we are optimistic for a good outcome, at the same time, we should prepare for the worst.”

In Punjab province, where nearly 100 cases of the coronavirus have been reported, officials announced a three-day lockdown, with all parks, malls and restaurants closed until Tuesday. Media outlets published photos of unarmed security forces guarding a new isolation facility in Lahore city. In Khyber-Pakhtunkhwa, a partial lockdown has also been instituted for the next three days, with all shopping malls and restaurants closed.

The government decided Saturday to ban all international arriving flights for 14 days, but the national carrier, Pakistan International Airlines, was allowed to bring back several of its planes from abroad, including one from London carrying Shahbaz Sharif, the opposition leader from the Pakistan Muslim League (N). He has been in London visiting his ailing brother, former prime minister Nawaz Sharif.

On Sunday, officials at the U.S. Embassy in Islamabad, the capital, said they were “aware” of reports from Pakistani health authorities that an unidentified embassy employee had been infected with the virus after landing at the international airport. They declined to provide further information, citing privacy reasons. Pakistani media reported that the individual was being treated in an isolation ward at the embassy.

Pakistan’s army chief, Gen. Qamar Javed Bajwa, ordered the army on Saturday to step up its assistance to civil authorities and urged all Pakistanis to take precautions to help curb the virus. The army is the most powerful institution in Pakistan, with a history of intervening in civilian power. Bajwa has emphasized his deference to civilian authority and desire to help in emergencies.

The army has said it will open all military hospitals and health facilities nationwide to assist in testing and treating virus cases.

Khan and his aides appealed to international financial institutions to write off loans to Pakistan and other developing countries to allow them to use more resources to fight the virus. Pakistan has a huge foreign debt, and Khan has struggled to implement economic austerity measures to bring it down.

Pakistan shares a border with China, and there is constant travel by workers, students and others between the two countries. A first, no Pakistani students were allowed to return after the virus broke out, and no cases were reported until Feb. 26, when a man in Karachi tested positive after returning from Iran.

Several days later, authorities began reporting a sharp surge in cases among pilgrims returning from Iran across the border at Taftan, Baluchistan, even after they had been held in quarantine there for 14 days. The three fatalities from the coronavirus as of Sunday night were pilgrims who returned from Iran or Saudi Arabia.

In the past several weeks, the rate of reported infections has risen sharply. As of Saturday, there were more than 290 confirmed cases in Sindh, more than 100 in Baluchistan, more than 150 in Punjab, 31 in Khyber-Pakhtunkhwa, 55 in Gilgit-Baltistan, 11 in Islamabad and one in Kashmir.

As of this weekend, health officials said a 3,000-room quarantine center has been set up in Multan, a city in Punjab, for infected pilgrims who returned from Iran. They said it has 171 isolation rooms. After screening there, patients will be sent to a new general hospital for treatment, they said.

Hussain reported from Islamabad, Pakistan. Haq Nawaz Khan in Peshawar, Pakistan, contributed to this report.