The US is "rapidly" making plans to evacuate Afghans who worked for the American military ahead of September's troop pullout, a top general has said.

Joint Chiefs Chairman Gen Mark Milley said a "significant" number of interpreters and other employees could be targeted by Taliban militants.

As many as 18,000 Afghan nationals have applied for US visas to immigrate to the US under a special programme.

But the scheme has been hit by delays, with applicants waiting for years.

"We recognise that there are a significant amount of Afghans that supported the United States and supported the coalition, and that they could be at risk," Gen Milley said in remarks his office released on Thursday.

"A very important task is to ensure that we remain faithful to them, and that we do what is necessary to ensure their protection and, if necessary, get them out of the country if that is what they want to do.

"There are plans being developed very, very rapidly here, not just interpreters but a lot of other people that have worked with the United States."

He added that the Department of State was overseeing the issue, without providing any further details.

In April, President Joe Biden said American troops would leave by 11 September, after 20 years of military involvement in Afghanistan. "It is time to end America's longest war," Mr Biden said.

There are at least 2,500 US troops in the country as part of the 9,600-strong Nato Afghan mission.

US and Nato officials have recently said that the Taliban, a hardline Islamist movement, has so far failed to live up to commitments to reduce violence in Afghanistan.