Afghan forces on Sunday handed over Bagram air base — once the U.S. military’s most important airfield in the country — to the Taliban, a district chief told the AP. The air base holds a prison containing 5,000 inmates.

Several other countries that had retained a diplomatic presence in Kabul even as Taliban gains accelerated began withdrawing their staff. The British ambassador will be airlifted from Afghanistan by Monday evening, the Sunday Telegraph newspaper reported. Iranian officials said its embassy in Kabul would be evacuated by Monday, according to Reuters.

The Danish and Norwegian embassies also recently said they would suspend operations and move staff out of the country.

President Biden on Saturday had announced that more troops would be sent to the capital to assist the departure of Americans there, expanding the number of troops sent to Kabul to 5,000. That includes an additional 1,000 troops that had been held at the ready in Kuwait, and at least 650 who had stayed behind in Afghanistan with the mission of protecting the U.S. Embassy and airport after the United States began withdrawing its military.

Afghan provincial capitals overrun by the Taliban as of Aug. 15 (Laris Karklis/The Washington Post)

The Pentagon has declined to call the deployment a combat mission. Pentagon spokesman John Kirby said troops have been deployed with machine guns, mortars and other heavy weapons with authorization to defend themselves if attacked.

Blinken was pressed by multiple television hosts Sunday about why the U.S. withdrawal appeared haphazard — particularly given the decision to withdraw forces, then send them back in. Blinken denied being caught flat-footed.

“The president was prepared for every contingency as this moved forward,” he said. “We had those forces on hand and they were able to deploy very quickly again to make sure that we could move out safely.”

Blinken and Defense Secretary Lloyd Austin will brief U.S. lawmakers about developments in Afghanistan on Sunday.

British lawmakers will also be recalled from recess next week to discuss the “deteriorating situation in Afghanistan,” Sky News reported.

Biden has warned that any moves by the Taliban that threaten American personnel or interests in the country would face a “swift and strong” response by the U.S. military.

The fall of Mazar-e Sharif on Saturday came as the Taliban appeared to have gained control of the province of Logar, an important gateway to the capital. Militants Saturday also captured the capital of Paktika, an eastern province bordering Pakistan, where local leaders fled for Kabul after surrendering.

Helicopters are landing at the U.S. Embassy in Kabul on Sunday as diplomatic vehicles leave the compound. (Rahmat Gul/AP)

As the last major city in Afghanistan still in government control, Kabul has been overrun by Afghans fleeing oppressive militant rule as the country faces a humanitarian disaster. Families who had flocked to Kabul were selling their possessions in an attempt to raise money amid reports that ATMs had stopped dispensing cash.

At the airport, people who had provided help to Western governments were seen on television news footage swarming visa processing centers, seeking a way out of the country. “We served for the American forces …” one person at the airport told ABC News. “They have to take care [of] us. It is our turn to be helped.”

Pietsch reported from Seoul. Claire Parker and John Hudson in Washington contributed to this report, which has been updated.