Joe Biden is sticking by his plan to withdraw US troops from Afghanistan by the end of the month, defying international pressure, including from key European allies, to allow more time for evacuations.

The US president’s decision caps days of uncertainty about the fate of the August 31 deadline for the final pullout of American military from Afghanistan. It comes despite growing concerns about the security situation around Kabul airport and the chaotic effort to evacuate thousands of foreign nationals and Afghans out of the country.

Jen Psaki, the White House press secretary, said Biden had confirmed during a virtual meeting of G7 leaders on Tuesday that the US was “currently on pace to finish” by August 31, and “made clear that with each day of operations on the ground, we have added risk to our troops with increasing threats from Isis-K”.

Biden did note “that completion of the mission by August 31 depends on continued co-ordination with the Taliban, including continued access for evacuees to the airport”, Psaki added, and “asked the Pentagon and the state department for contingency plans to adjust the timeline should that become necessary”.

She said at a later briefing with reporters that civilian evacuations would likely end prior to August 31 in order to give the military time to “wind down” its own presence.

The US president had come under pressure from Britain, France and Germany in particular to extend the US mission in Afghanistan beyond August 31, including during Tuesday’s G7 meeting.

The meeting came as the Taliban blocked the road to Kabul airport for Afghans, which threatens to strand those vulnerable to reprisals from the Islamist movement.

Zabihullah Mujahid, the Taliban spokesman, said the group would allow foreigners to leave through the airport but ordered Afghans not to go to the airport because of the chaotic crowds and the risk of stampedes, urging them to return to their jobs and homes.

He reiterated that all foreign evacuations had to be completed by August 31. “We don’t allow it any more and call on them to evacuate by that date,” he said. “They [western states] have the possibilities, they have the planes, the airfield is with them and they can evacuate people by that date.”

Boris Johnson, the UK prime minister who chaired the G7 meeting, said leaders had agreed a joint approach to put pressure on the Taliban to allow safe passage out of the country for Afghans even after August 31.

“The number one condition that we are setting as the G7 is that they have got to guarantee right the way through, through August 31 and beyond, safe passage for those who want to come out,” he said.

Johnson insisted the “immediate phase of evacuation is actually being a very considerable success by the military” but — along with French president Emmanuel Macron and German chancellor Angela Merkel — he wanted more time to get people out of Kabul.

Charles Michel, the European Council president, said several G7 leaders expressed concerns about the August 31 deadline during the meeting.

Washington has come under mounting criticism about the manner of its withdrawal and the mayhem around the evacuation process. The Taliban seized power 10 days ago after a lightning blitz across the country following the drawdown of US troops.

CIA director William Burns met earlier this week with Taliban co-founder Mullah Abdul Ghani Baradar — the highest person-to-person meeting since the Islamist group returned to power — according to a person familiar with the encounter. The CIA declined to comment.

The fear for many Afghans is that the Taliban will persecute those who have worked for western militaries, such as translators and drivers, as well as journalists and critics of the Islamist group.

Mujahid rejected suggestions that the Taliban was searching for individuals associated with the old regime, saying the group had announced a general amnesty. He said hospitals and schools had reopened, and banks were due to reopen on Wednesday.

Afghans at the airport had nothing to fear, Mujahid added. “We guarantee their security.”

Many of those scrambling to board flights are among the most-educated members of the population, who are needed to keep the economy and public services running.

Western officials have expressed concerns that the security situation is in danger of deteriorating as the August 31 deadline looms.

“As we get closer to the deadline, I think it’s correct to say the security risk goes up,” Ben Wallace, UK defence secretary, told Sky News. “It just gets more and more dangerous as add-on groups and other terrorist groups such as Isis would like to be seen taking credit, or would like to be seen to chase the west out of the airport.”

The US military reported its biggest day of airlifts out of Afghanistan on Tuesday, with 37 US flights taking 12,700 people out of the country in 24 hours. Including coalition flights, 21,600 people were evacuated in the same period, the White House said. To date, approximately 4,000 American passport holders and their families have been evacuated from Afghanistan, according to the Pentagon.

Additional reporting by Aime Williams and Katrina Manson in Washington