While Afghan cities fells like dominoes to the Taliban, halfway across the globe in Washington, finger-pointing dominated the discourse over the rapid fall of Afghanistan's government.

US Secretary of State Antony Blinken was asked Sunday about the scenes of chaos in the capital Kabul, by ABC News reporter Johnathan Karl.

"Just last month, President Biden said that under no circumstance, and those were his words, under no circumstance would the US personnel, embassy personnel be airlifted out of Kabul in a replay of the scenes that we saw in Saigon (Ho Chi Minh City) in 1975," he said.

"So, isn't that exactly what we're seeing now? I mean, even the images are evocative of what happened in Vietnam."

"Let's take a step back," Blinken said. "This is manifestly not Saigon."

US President Joe Biden had said at a July 8 news conference that, "There's going to be no circumstance where you're going to see people being lifted off the roof of (an) embassy of the United States from Afghanistan."

The US ambassador to Afghanistan and some of his staff were seen fleeing Kabul with the American flag Sunday, as the Pentagon increased the number of troops by 1,000 to 6,000 to help with the evacuation. Biden had said the US would largely complete its withdrawal by Aug 31, but the events of the past week have likely changed that timetable.

Ambassador Ross Wilson was seen with the flag arriving at Kabul Airport, as other Americans still in the mountainous country that straddles central and south Asia were ordered to shelter in place as shots were fired at the city's airport.

Biden said Saturday that former president Donald Trump "left the Taliban in the strongest military position since 2001".

"When I came to office, I inherited a deal cut by my predecessor — which he invited the Taliban to discuss at Camp David on the eve of 9/11 of 2019 — that left the Taliban in the strongest position militarily since 2001 and imposed a May 1, 2021, deadline on US forces," Biden said in a statement.

"Shortly before he left office, he also drew US forces down to a bare minimum of 2,500. Therefore, when I became President, I faced a choice — follow through on the deal, with a brief extension to get our forces and our allies' forces out safely, or ramp up our presence and send more American troops to fight once again in another country's civil conflict."

Trump responded with his own statement Saturday, saying: "He ran out of Afghanistan instead of following the plan our Administration left for him — a plan that protected our people and our property, and ensured the Taliban would never dream of taking our Embassy or providing a base for new attacks against America.

"The withdrawal would be guided by facts on the ground," Trump said of the 2019 deal. "After I took out ISIS, I established a credible deterrent. That deterrent is now gone.

"The Taliban no longer has fear or respect for America, or America's power," Trump said. "What a disgrace it will be when the Taliban raises their flag over America's Embassy in Kabul."

The Taliban swept into Kabul on Sunday as the embattled president joined an exodus of citizens and foreigners, signaling the end of a costly two-decade US campaign to remake the country.

US Army General Mark Milley, chairman of the joint chiefs of staff told senators Sunday that a previous assessment of how soon terrorist groups will likely regroup in Afghanistan will be expedited because of the current situation, reported Axios, citing three sources on the phone call.

As heavily armed Taliban fighters fanned out across the capital, and several entered Kabul's abandoned presidential palace, Suhail Shaheen, a Taliban spokesman and negotiator, told The Associated Press that the group would hold talks in the coming days aimed at forming an "open, inclusive Islamic government".

Also, a Taliban commander claimed he spent eight years in Guantanamo Bay in a triumphant speech from inside the palace.

Al-Jazeera livestreamed the news conference from inside the palace, which showed a group of Taliban fighters sitting at the president's desk before one claimed he was a former inmate of the US-controlled detention center in Cuba.

Taliban spokesman Mohammad Naeem said that the war was over and that the group was not looking to increased hostilities.

"We have reached what we were seeking, which is the freedom of our country and the independence of our people," he said. "We will not allow anyone to use our lands to target anyone, and we do not want to harm others.

"We do not think that foreign forces will repeat their failed experience in Afghanistan once again," Naeem said.

Helicopters hovered above Kabul through the day to evacuate personnel from the US embassy. Smoke rose near the compound as staff destroyed documents, and the American flag was lowered.

As the Taliban closed in, President Ashraf Ghani flew out of the country.

"The former president of Afghanistan left Afghanistan, leaving the country in this difficult situation," said Abdullah Abdullah, the head of the Afghan National Reconciliation Council and a longtime rival of Ghani. "God should hold him accountable."

Ghani later posted on Facebook that he left to avert bloodshed in the capital, without providing his destination.

The Taliban seized nearly all of Afghanistan in a little more than a week, despite the billions of dollars spent by the US and NATO over nearly 20 years to build up Afghan security forces.

An Afghan university student described feeling betrayed as she watched the US embassy evacuation.

"You failed the younger generation of Afghanistan," said Aisha Khurram, 22, who is now unsure of whether she will be able to graduate in two months. She said her generation was "hoping to build the country with their own hands. They put blood, efforts and sweat into whatever we had right now."

Earlier Sunday, the Taliban seized Jalalabad before marching on Kabul. Afghan forces at Bagram Air Base, home to a prison housing 5,000 inmates, surrendered to the Taliban, according to the Bagram district chief. The prison at the former US base held both Taliban and Islamic State group fighters.

The Associated Press contributed to this story.