London, July 2: Defence officials say the last US and Nato forces have left Afghanistan's Bagram airbase, the centre of the war against militants for some 20 years.

The pull-out could signal that the complete withdrawal of foreign forces from Afghanistan is imminent.

President Joe Biden has said US forces will be gone by 11 September. But the withdrawal from the sprawling base, north of Kabul, comes as the main jihadist group, the Taliban, advances in many parts of Afghanistan.

The 11 September deadline is the anniversary of the attacks on America in 2001, which killed nearly 3,000 people.

The attacks were carried out by al-Qaeda, an international jihadist group then based in Afghanistan with the support of the Taliban, who had been in control of the country since the 1990s. A US-led coalition invaded Afghanistan later that year to defeat both groups.

America now wants to end its longest war with its huge cost in human lives and vast expense and is leaving security to the Afghan government.

Some 2,500-3,500 US troops were thought to be still in Afghanistan until recently, and they are due to depart along with some 7,000 other coalition troops, leaving fewer than 1,000 American soldiers in the country.

Meanwhile, a resurgent Taliban, buoyed by the expectation of the foreign withdrawal, has overrun dozens of districts, amid fears that a new civil war could erupt after the departure of foreign forces.