The Prime Minister will unveil a “bespoke” resettlement scheme for vulnerable Afghans as efforts to get British nationals and other support staff back to the UK continue.

No 10 said Boris Johnson would give more information about the refugee scheme in the coming days, with the policy anticipated to be focused on helping women and girls.

In Afghanistan, British armed forces numbers are to be bolstered to 900, with a further 200 announced by the Ministry of Defence on Monday.

They will be involved in the push to bring UK nationals home and secure the safety of selected Afghans, an effort that has intensified since the Taliban took Kabul following their lightning offensive which has shocked the West.

The decision to send in additional troops follows frantic scenes at Kabul airport that left seven people dead, including some who fell from a departing US military transport jet.

However, in a defiant statement, US President Joe Biden said he stood “squarely behind” the decision to withdraw American troops from Afghanistan, vowing not to let the war enter a “third decade”.

Despite Allied intentions to withdraw armed forces entirely by next month, both the US and the UK are sending in further troops to assist with evacuation efforts, a move that armed forces minister James Heappey said would make controlling Kabul airport easier.

The Afghanistan veteran, who said the UK Government had been working on the premise that Kabul would hold until next year, told BBC Newsnight: “The airport is a focal point for many people who are very desperate and unsurprisingly there have been a number of incursions into the airfield over the last 24 hours, which has required it to be closed at various stages.

“But the arrival of the US 82nd Airborne and 2 Para from the United Kingdom’s Parachute Regiment should mean we are able to secure the airfield more consistently over the coming days.”

Mr Johnson is expected to announce a resettlement scheme to allow fleeing Afghans to set-up home in the UK shortly, according to No 10.

The Telegraph reported that the concept could be similar to that used to take in Syrian refugees in 2015, which saw women with children, people with serious medical conditions and survivors of torture prioritised.

The paper said the Government had yet to determine how many Afghan refugees could benefit from a similar initiative, but the Syrian programme enabled 20,000 to be resettled over six years.

Mr Heappey, asked whether women’s rights activists could be among those to be welcomed to Britain, said: “It is not in my gift as the minister for the armed forces to say here and now, yes they should, but I know their cries are not falling on deaf ears.”

With the refugee scheme in the pipeline, the Home Office also announced that restrictions on the Afghan Relocations and Assistance Policy (Arap) – the programme to resettle Afghan nationals who have supported British efforts in the central Asian country – have been eased.

The department has removed the requirement for applications to be made in Afghanistan, allowing those who are able to flee the Taliban-occupied area to do so without compromising their eligibility to settle in the UK.

With Afghan interpreters hiding in basements out of fear of being killed by the Taliban, former British Army officer Charlie Herbert told BBC Newsnight that efforts to rescue those who had supported UK troops should be a priority.

“If we can salvage some dignity from this humiliation, it would be to get those people out of Kabul as quickly as we can,” said the former major general.

A Downing Street spokeswoman said: “The UK team in Afghanistan is working around the clock in incredibly difficult circumstances to help British nationals and as many others as we can get to safety as soon as possible.

“At the same time, we are bringing together the international community to prevent a humanitarian crisis emerging in Afghanistan – it’s in everyone’s interest not to let Afghanistan fail.

“That means providing whatever support we can to the Afghan people who have worked so hard to make the country a better place over the last twenty years and who are now in need of our help.”

Officials said Mr Johnson is calling for high-level international discussions on the unfolding crisis, including using the UK’s G7 presidency to call a virtual meeting in the “coming days”.

He wants G7 leaders to focus on ensuring Afghanistan does not once again become a source of international terrorist threats, No 10 said.

There will also be an effort to secure support for the people of Afghanistan, including through increased humanitarian assistance and agreeing expectations of whatever government emerges in Afghanistan.

Downing Street wants the five permanent members of the United Nations Security Council (UNSC) – which, as well as the UK, includes the US, China, France and Russia – to meet following the full gathering that took place on Monday.

Following the Prime Minister’s phone call with French president Emmanuel Macron, in which he raised the prospect of a G7 meeting, the UK and France are expected to work together on a joint UNSC resolution.

Foreign Secretary Dominic Raab has refused to rule out sanctions against the Taliban if they fail to co-operate internationally.