Boris Johnson is expected to use a G7 meeting to push for US president Joe Biden to extend the Kabul evacuation deadline beyond 31 August.
But a UK defence minister had admitted the Taliban may not allow evacuation effort to continue beyond the end of the month.
“We have been having these conversations with the Americans,” armed forces minister James Heappey said on Monday. “This isn’t just a decision that gets taken in Washington – the Taliban gets a vote on this as well.”
The minister told Sky News: “I think it’s far from certain that the Taliban are going to be willing to allow the international community to extend beyond the end of the month.”
Acknowledging that the Taliban had been an “effective partner” in the evacuations so far, Mr Heappey urged the militants to show “they want to be a part of the international system” by allowing the flights to continue.
The armed forces minister also admitted there is a “hard reality” that the UK will not be able to evacuate all the refugees it hopes to from Kabul airport.
“We will get out as many as we possibly can but we have been clear throughout that there is a hard reality that we won’t be able to get out everybody that we want to,” he said – adding that the flights were “not the only route to the UK”.
Foreign secretary Dominic Raab and defence Secretary Ben Wallace held talks with their Washington counterparts over the weekend to press home the desire for US troops to remain in Afghanistan beyond August in order to continue to secure the airport for flights.
The prime minister is due to use an emergency G7 summit on Tuesday to personally lobby Mr Biden on the issue. In a tweet, he said it was “vital that the international community works together to ensure safe evacuations”.
Foreign Office minister James Cleverly told BBC that the government would continue to try to convince the White House to extend the exit deadline. “Obviously the more time that we’ve got, the more people we can evacuate and that’s what we’re pushing for,” said Mr Cleverly.
But the US president signalled on Sunday that he did not want US armed forces to stay in the country beyond August. “Our hope is that we don’t have to extend but there are discussions going on about how far we are.”
Labour leader Sir Keir Starmer has written to Mr Johnson calling for more details on how the UK is planning the next stages of the rescue mission.
Sir Keir asked whether Mr Johnson had “spoken personally” to Mr Biden – and whether the UK was working on a contingency plan with Nato allies to “hold Kabul airport without US troops”.
Government officials said there is “no fixed date” on when the UK will withdraw but it is feared that without US boots on the ground, the remaining allied forces would be unable to secure Hamid Karzai International Airport.
The armed forces minister said on Monday that the airlift from Kabul airport is “underpinned” by US forces and it could not happen without them.
“It is certainly the case that the mission in Kabul this week is fundamentally underpinned by a US presence,” Mr Heappey told Sky News. “So, there is a hard reality that there would be no international airlift without the way that the US are underpinning it.”
The minister also said there is “every reason” the Taliban should be proscribed as a terrorist organisation. “I think that there is every reason to think that they should be,” he told Times Radio. “But by the same token they are a group of people with whom we are very much needing to work with right now.”
The Ministry of Defence confirmed that 5,725 people have been repatriated since rescue efforts began on August 13, with 3,100 of them Afghan individuals and their families.
On Sunday, 1,721 people were airlifted from Kabul by the Royal Air Force across eight flights.
Brigadier Dan Blanchford, the most senior UK military officer on the ground in Kabul, said British troops had “witnessed some harrowing scenes”, with at least seven Afghan civilians confirmed to have died outside the airfield gates amid chaotic crowds.
It has been reported that as many as 20 people have been killed in the past week while trying to get into the departure point.
Brigadier Blanchford, Commander Joint Forces Operations, said UK armed forces were “redoubling” their efforts to “speed up the process” of helping people make their exit – with the Times reporting that the RAF hopes to fly out as many as 2,000 people per day.
The newspaper also said the military will be extending the deadline for the last RAF evacuation, pushing it back from Tuesday to Friday or Saturday, with the evacuation programme expanded from 6,000 people eligible to come to Britain to more than 12,000.
