The United States has deployed extra military resources to protect American and coalition forces withdrawing from Afghanistan.

Heavy bombers and fighter jets will be deployed to safeguard troops and civilian contractors.

The US and Nato have had a presence in Afghanistan for almost 20 years.

US President Joe Biden has set the withdrawal deadline for 11 September - the 20th anniversary of the 9/11 attacks that sparked the war.

But the withdrawal comes amid escalating violence, with Afghan security forces on high alert for reprisal attacks.

The Taliban have warned they are no longer bound by an agreement not to target international troops.

Under a deal signed last year between the militants and then-President Donald Trump, foreign forces were to have left by 1 May while the Taliban held off attacking international troops.

What has been deployed?

Six B-52 long range bombers and 12 F-18 fighters have been deployed to protect the departing contingents of 2,500 US service members and 16,000 civilian contractors, said Mark Milley, Chairman of the Joint Chiefs of Staff.

General Milley added that while Taliban insurgents were launching between 80 and 120 attacks every day against Afghan government targets, there had been no attacks against US and coalition forces since the withdrawal began on 1 May.

"Less than one week in, the drawdown is going according to plan," Defence Secretary Lloyd Austin told reporters.

Why are US forces in Afghanistan?

On 11 September 2001, attacks in America killed nearly 3,000 people. Osama Bin Laden, the head of Islamist militant group al-Qaeda, was quickly identified as the man responsible.

The Taliban, radical Islamists who ran Afghanistan and protected Bin Laden, refused to hand him over. So, a month after 9/11, the US launched air strikes against Afghanistan.

As other countries joined the war, the Taliban were quickly removed from power. But they didn't just disappear - their influence grew back and they dug in.

Since then, the US and its allies have struggled to stop Afghanistan's government collapsing, and to end deadly attacks by the Taliban.