US President Joe Biden has said the drawdown of US troops from Afghanistan is on track but will not be done in the next few days.
Mr Biden, speaking to reporters at the White House, said he was confident that Afghan leaders had the capacity to sustain the government but was concerned about internal issues
We're on track exactly as to where we expect to be," he said, following growing speculation the final contingents were due to leave within the next few days.
Mr Biden has set a deadline of 11 September for the final pull-out of the few remaining troops, following 20 years of war.
Earlier, the US military officially handed over Bagram Air Base, a spokesman for Afghanistan's defence ministry has said, after the last foreign forces left the sprawling complex as part of their withdrawal from the country.
"The American and coalition forces have completely withdrawn from the base and henceforth the Afghan army forces will protect it and use it to combat terrorism," defence ministry spokesman Fawad Aman said on Twitter.
A US defence official had also confirmed that all US and NATO troops had left the biggest air base in Afghanistan.
Bagram Air Base served as the linchpin for US operations in the rugged country, where the long war against the Taliban and their Al-Qaeda allies was fought with air strikes and resupply missions from the airfield.
"All coalition forces are off Bagram," said the official, without specifying when the last foreign troops left the base, 50km north of Kabul.
The Taliban said it welcomed and supported the latest phase of the troop pullout.
"Their full withdrawal will pave the way for Afghans to decide about their future between themselves," a spokesman said
The US military and NATO are in the final stages of winding up involvement in Afghanistan, bringing home an unspecified number of remaining troops by a deadline of 11 September.
The Taliban have launched relentless offensives across Afghanistan in the past two months, taking dozens of districts as Afghan security forces have largely consolidated their power in the country's major urban areas.
The ability of Afghan forces to maintain control over the vital Bagram airfield will likely prove pivotal to maintaining security in the nearby capital Kabul and keeping pressure on the Taliban.
Over the years, the mini-city has been visited by hundreds of thousands of US and NATO service members and contractors.
It boasted swimming pools, cinemas and spas - and even a boardwalk featuring fast-food outlets such as Burger King and Pizza Hut.
The base also hosted a prison that held thousands of Taliban and jihadist inmates.
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Bagram was built by the US for its Afghan ally during the Cold War in the 1950s as a bulwark against the Soviet Union in the north.
Ironically, it became the staging point for the Soviet invasion of the country in 1979, and the Red Army expanded it significantly during their near decade-long occupation.
When Moscow pulled out, it became central to the raging civil war - it was reported that at one point the Taliban controlled one end of the 3km runway and the opposition Northern Alliance the other.
In recent months, Bagram has come under rocket barrages claimed by the so-called Islamic State, raising
fears that militants are already eyeing the base for future attacks.
The NATO-led non-combat mission aimed to train Afghan forces into ensuring their country's security after the departure of foreign forces.
As of February 2021, there were about 9,500 foreign troops in Afghanistan, of which the US made up the largest contingent of 2,500.
So far Germany and Italy have both confirmed the full withdrawal of their troops.
Dr Edward Burke, Associate Professor in International Relations at the University of Nottingham, described the military situation in Afghanistan as 'grave'.
Upon seeing the Taliban seizing more territory in the country, as they have been over the last few weeks, Dr Burke said he does not expect a swift collapse of the Afghan military any time soon.
"Some people are making a lot of Vietnam analogies that this is sort of Saigon all over again and there will be a quick Taliban victory" he told RTÉ News.
Dr Burke said there is a "resilient" part of the Afghan security forces that will keep fighting during an expected escalation of conflict over the next couple of months.
"There are very large political groupings and actions within the Afghan security ministries, within the army and the police who will not give in easily because they believe that the consequences would be so disastrous for them if there is a Taliban takeover of the country" he added.
