US, UK and other western forces have helped to secure Kabul’s international airport, allowing the RAF to begin mass airlifts out of the Afghan capital, the commander of Britain’s evacuation effort has said.

V-Adm Ben Key, the commander of joint operations, said there was now “considerably greater stability” on the ground, ending the “distressing scenes” of Monday when some desperate Afghans clung to military aircraft as they took off.

The plan was to “create capacity” for “around 1,000 outward passengers every day,” he added, in the hope of evacuating an estimated 3,000 Britons and dual nationals still the country, plus a further 3,000 Afghans eligible for resettlement in the UK.

But the British commander acknowledged that the Taliban could close the airport at any time, and said: “We may well find that the security situation on the ground may make it untenable to continue to evacuate other people.”

Chaos at the airport after the sudden collapse of the Afghan government over the weekend, following the withdrawal of US and Nato troops, means the RAF has been able to airlift only a few hundred people so far.

Video footage showed some people appearing to fall from a US military plane after it had taken off, unable to hang on.

On Tuesday the UK foreign secretary, Dominic Raab, said 350 more people – British nationals as well as Afghans who worked for UK forces and their families – had been airlifted out of Kabul in the last 24 hours.

On Monday the Foreign Office had faced criticism for concentrating on evacuating diplomats “on the first plane out” while leaving military personnel to pick up the pieces on the ground.

A frustrated defence secretary, Ben Wallace, told colleagues that young soldiers were sometimes “having to process visa applications of incredible complexity at speed”, and there would be “a reckoning” for the Foreign Office.

Key said nearly 900 British military personnel were now on the ground and that having secured the site, Foreign Office and other officials would be coming in to help process people on to planes.

“The first thing we had to do is to achieve security, and that is a military activity, and that we have now done. And cross-Whitehall colleagues are now joining us to undertake their specific roles,” Key said in a pooled interview.

Military personnel had been helping to process people, Key said. “In the meantime of course we are going to see what we can do,” although he added “as soldiers, sailors and air personnel, that’s not the roles we are trained to do.”

The British operation is working to a broad deadline of 31 August, a date set by the US president, Joe Biden, for the withdrawal of US forces, currently numbering around 6,000, to conclude the evacuation.

Military experts say it would be easy for the Taliban to close the airport by firing mortars or other shells at the runway, because they control the area around it. “We don’t know how long we have. We have to maximise every day as best we can,” Key said.