President Joe Biden has accepted a Pentagon recommendation to remove US troops from Afghanistan by an Aug. 31 deadline, an administration official told Reuters on Tuesday.

Biden also asked for contingency plans to stay longer, should it be necessary, the official said.

The Pentagon recommendation reflects increasing security concerns at the Kabul airport, where American citizens and at-risk Afghans are being evacuated.

Washington is telling the Taliban the Aug. 31 deadline is contingent on the group's cooperation in facilitating evacuations, the official added.

Biden was set to speak later on Tuesday.

Earlier on Tuesday, the Pentagon said there had been no change so far in its plan to meet the Aug. 31 deadline and that it intended to withdraw US troops by then.

Pentagon spokesman John Kirby said the Pentagon believes it has the ability to get all Americans who want to leave out of Afghanistan by Aug. 31.

"We're absolutely still aiming towards the end of the month," Kirby said, while adding that the Pentagon may need additional bases to house evacuees from Afghanistan.

Kirby said "several thousand" Americans have been evacuated from Afghanistan but declined to give a more specific figure. He also said he was unable to provide the percentage of Americans in Afghanistan who have now been evacuated.

"The president's direction has been to complete this withdrawal, this evacuation and withdrawal, by the 31st of August. That is the direction that we are operating under and therefore, that is driving a lot of our plans," Kirby said.

Afghanistan's new Taliban rulers said on Tuesday they wanted all foreign evacuations from the country completed by an Aug. 31 deadline and they would not agree to an extension as Group of Seven leaders met to discuss the crisis.

Western troops have been working frantically to get foreigners and Afghans onto planes and out of the country and Biden has faced growing pressure from allies to negotiate more time for the airlift.