The Taliban have agreed to allow “safe passage” from Afghanistan for civilians struggling to join a US-directed airlift from the capital, President Joe Biden’s national security adviser said.

A deadline for the completion of evacuation of Americans, Afghan allies and others are yet to be finalised.

Jake Sullivan on Tuesday acknowledged reports that some civilians were encountering resistance – “being turned away or pushed back or even beaten” – as they tried to reach the Kabul international airport.

But he said “very large numbers” were reaching the airport and the problem of the others was being taken up with the Taliban.

Pentagon officials said that after interruptions on Monday, the airlift was back on track and being accelerated despite weather problems, amid regular communication with Taliban leaders.

The White House said 13 flights Tuesday airlifted 1,100 US citizens, permanent residents and their families from the Kabul airport, adding that the pace was expected to pick up Wednesday and through the week.

The State Department said it was sending John Bass, a former ambassador to Afghanistan, to manage the evacuation operation in Kabul, and the Pentagon said it will send Army Maj. Gen. Christopher Donohue, a special operations officer and current commander of the 82nd Airborne Division, to take command of airport security operations.

Pentagon spokesman John Kirby disclosed that U.S. officers were speaking with Taliban commanders “multiple times a day” about avoiding conflict at the airport.

Biden has said he wants the evacuation completed by August 31. Sullivan declined to say whether that deadline would hold.

At the White House, Sullivan said U.S. officials were engaged in an “hour by hour” process of holding the Taliban to their commitment to allow safe passage for civilians wishing to leave the country.

Asked whether the Biden administration recognizes the Taliban as the legitimate rulers of Afghanistan, Sullivan said it was too soon to say and that the Taliban’s record of adhering to international human rights standards “has not been good.”

Overnight at the airport, nine Air Force C-17 transport planes arrived with equipment and about 1,000 troops, and seven C-17s took off with 700-800 civilian evacuees, including 165 Americans, Army Maj. Gen. William Taylor told a Pentagon news conference. The total included Afghans who have applied for Special Immigrant Visas and third-country nationals, he said.

The goal is to ramp up to one evacuation flight per hour by Wednesday, with 5,000 to 9,000 evacuees leaving per day, Taylor and Kirby said.

Taylor said that more than 4,000 US troops are now at the airport. That number is expected to top 6,000 in coming days – more than twice as many as in all of Afghanistan when Biden announced in April he would be ending the U.S. war and pulling out all troops.