KABUL — Taliban forces entered Kabul through the city’s four main gates Sunday morning, according to two Afghan security officials and civilian eyewitness accounts. The Islamist group is poised for a full return to power, two decades after a U.S.-led coalition invaded Afghanistan.

In a sign that the government has collapsed, Afghan President Ashraf Ghani fled the country, Abdullah Abdullah, the head of the Afghan High Council for National Reconciliation, confirmed in a video shared online.

Taliban spokesman Zabiullah Mujahid said in a statement that the group’s fighters had been instructed not to push further into the city with force. The militants had made recent gains after negotiating with local leaders. “We want to enter Kabul with peace, and talks are underway” with the government, he said.

Negotiators representing the national government are headed to Doha, Qatar, on Sunday to discuss an agreement with the Taliban’s political leadership, a senior official close to Ghani said. Members of the militant group were also at the presidential palace for talks on Sunday afternoon, according to two Afghan officials.

“There is an agreement that there will be a transitional administration for orderly transfer of power,” said the acting interior minister, Abdul Satar Mirzakwal, on Sunday. He added that security forces were being deployed across Kabul to ensure order.

The Taliban’s lightning-quick advance to the Afghan capital came as helicopters landed at the U.S. Embassy early Sunday and armored diplomatic vehicles were seen leaving the area around the compound, the Associated Press reported. Diplomats scrambled to destroy sensitive documents, sending smoke from the embassy’s roof, the AP said, citing anonymous U.S. military officials.

U.S. personnel at the U.S. Embassy in Afghanistan are being relocated to the airport to “ensure they can operate safely and securely” as the Taliban encircle Kabul, Secretary of State Antony Blinken told ABC News on Sunday.

Mere hours before, the Taliban had captured the city of Jalalabad, adding the eastern provincial capital to the large swaths of the country the militants control. The fall came just hours after the Taliban seized Mazar-e Sharif — a northern city long seen as an anti-Taliban stronghold.

The Taliban’s recent takeovers have significantly pushed forward Washington’s forecast for how quickly the Afghan government could collapse. As of last week, the U.S. military had estimated a collapse within 90 days. In June, American officials had forecast that a collapse would take six to 12 months.

Blinken took to the Sunday shows to defend the Biden administration’s decision to withdraw from Afghanistan, arguing that the Taliban’s current offensive would have happened even if U.S. forces remained in Afghanistan.

“If the president had decided to stay, all gloves would’ve been off, we would’ve been back at war with the Taliban, attacking our forces, the offensive you’ve seen throughout the country almost certainly would’ve proceeded,” Blinken told NBC.

The Taliban’s capture of Jalalabad, close to Afghanistan’s border with Pakistan, came with minimal resistance after militants and local elders negotiated the fall of the city’s government. Leaders in Jalalabad were given safe passage from the city, according to Reuters.

Both Bagram and Sorobi districts in Kabul province also surrendered without shots being fired, according to an official, who added that the militants had made “political deals” with local leaders.

On Aug. 14, President Biden approved additional military forces to help safely draw down the American embassy and remove personnel from Afghanistan. (Reuters)

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 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.

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 on Saturday also captured the capital of Paktika, an eastern province bordering Pakistan, where local leaders fled for Kabul after surrendering.

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.