The Biden administration scrambled to put a botched evacuation of Afghanistan back on track on Tuesday as it admitted its original plans needed to be changed following a day of chaos and violence at Kabul’s international airport.

In an attempt to project competence after the Taliban swiftly took control of the country in the face of a crumbling Afghan military, the White House said it had secured the airport and would speed up the pace of evacuations in the days ahead.

Jake Sullivan, president Joe Biden’s national security adviser, told reporters the administration had been “clear eyed” about the risk that the Islamist group would “end up in control of Afghanistan” but conceded that “we did not anticipate it would happen at the speed” at which it did.

“Yes, there were chaotic scenes [on Monday] but . . . even well-drawn plans don’t survive first contact with reality, and they require adjustments, and we’ve made those adjustments,” Sullivan added.

However, the administration stood by its decision to pull troops out of the country after a two-decade long war, fulfilling a pledge made last year on the campaign trail by Biden, who first began calling for a withdrawal when he was vice-president in the Obama administration.

Sullivan said the images of people clinging to and in some cases falling from US military aircraft as they took off from Kabul airport were “heartbreaking”. But he added: “President Biden had to think about the human costs of the alternative path as well, which was to stay in the middle of a civil conflict in Afghanistan.”

Sullivan said US officials were talking directly with the Taliban about ensuring the safety of civilians seeking to access the airport, just hours after the Islamist group’s leaders triumphantly addressed a throng of Afghan reporters in the country’s capital.

He said the administration had “received reports of people being turned away” from the airport by the Taliban “or even beaten” and that the US was trying to resolve those issues via a backchannel with the Islamist group. “We are concerned about whether that will continue to unfold in the coming days,” Sullivan added.

But he insisted that “as things stand right now, what we are finding is we are getting people through the gate”.

The Taliban said it would not seek revenge against government officials or Afghan soldiers, and that the group would respect the rights of women “within the limits of Islamic law”. The last time the Taliban was in power, they ruled Afghanistan with a brutal interpretation of Islam that largely extinguished women’s rights.

Earlier on Tuesday, the Pentagon said there would be about 4,000 troops on the ground in Kabul by the end of the Tuesday and that a US Air Force C-17 aircraft brought about 1,000 extra US soldiers into Hamid Karzai International Airport overnight.

The pace of evacuations would now pick up, Pentagon spokesperson John Kirby told reporters. Between 700 and 800 people were evacuated overnight, 165 of who were US citizens, while the remainder were a mixture of Afghan visa holders and other nationalities.

The scale of evacuation could reach between 5,000 and 9,000 people per day, he added. 

Kirby said there had been no hostile interactions with the Taliban at the airport, which remained secure. However, he declined to provide the number of casualties caused by US planes taking off with people clinging to the exterior, as seen in videos widely shared on the internet. 

Biden’s top advisers addressed the media on Tuesday as the president remained at his country retreat in Camp David. On Monday, the president returned briefly to the White House to address the unfolding crisis.

“I stand squarely behind my decision,” Biden said, defending his administration’s withdrawal of troops from Afghanistan. “I have learned the hard way that there was never a good time to withdraw US forces.”

Biden has faced criticism from within his own party over the administration’s handling of the troop withdrawal in Afghanistan. The New York Times reported that US spy agencies had warned this summer that the Afghan army could quickly collapse, despite repeated reassurances from Biden and his advisers that it had the resources and will to fight.

In response to a question about those intelligence reports, Sullivan said: “I’m not actually familiar with the intelligence assessments you’re describing, but I also don’t want to get into specific intelligence products.”

Senior Democratic lawmakers have already pledged congressional hearings to investigate why the US was not better prepared for an orderly withdrawal of its troops from Afghanistan.

Bob Menendez, the Democratic chair of the Senate’s foreign relations committee, said on Tuesday that he was “disappointed” that the administration had not understood the implications of a rapid US withdrawal. He also blamed former president Donald Trump for the “wholly inadequate agreement” it brokered with the Taliban.

“We are now witnessing the horrifying results of many years of policy and intelligence failures,” Menendez said in a statement.

Jack Reed, the Democratic chair of the Senate armed services committee, also said he would order hearings into “what went wrong”, but avoided apportioning blame.

Mark Warner, the Democratic chair of the Senate intelligence committee, has also called for a congressional probe, saying: “We owe those answers to the American people and to all those who served and sacrificed so much.”

Additional reporting by Stephanie Findlay in New Delhi