British Prime Minister Boris Johnson said on Wednesday the Taliban would be judged on their actions, not their words, after they sought to convince the world they would not seek revenge after seizing Afghanistan.

Addressing parliament, which was recalled from its summer break to discuss the situation in Afghanistan, Johnson ruled out any resumption of military action in the country and instead called on the United Nations to lead a humanitarian effort.

The Taliban have said they want peace, will not take revenge against old enemies and would respect the rights of women within the framework of Islamic law. But thousands of Afghans, many of whom helped foreign forces, are desperate to leave.

"We will judge this regime based on the choices it makes, and by its actions rather than by its words, on its attitude to terrorism, to crime and narcotics, as well as humanitarian access, and the rights of girls to receive an education," Johnson said.

"No matter how grim the lessons of the past, the future is not yet written. And at its bleak turning point, we must help the people of Afghanistan to choose the best of all their possible futures."

Britain has said it will welcome up to 5,000 Afghans during the first year of a new resettlement programme that will prioritise women, girls and religious and other minorities, part of Western plans to help those leaving the country.

"We will be ... doing everything we can to support those who have helped the UK mission in Afghanistan, and investing everything that we can to support the wider area around Afghanistan, and to do everything we can to avert a humanitarian crisis," Johnson said.

The speed to the Taliban's gains in Afghanistan after U.S.-led forces withdrew the bulk of their troops surprised the West, leaving many nations having to scramble to get their diplomats and those Afghans who had helped them out of the nation.

"The situation has stabilised since the weekend, but it remains precarious, and the UK officials on the ground are doing everything they can to expedite the movement of people, those that need to come out," Johnson said.

"I really think that it is an illusion to believe that there is appetite amongst any of our partners for a continued military presence or for a military solution imposed by NATO in Afghanistan.

"That idea ended with the combat mission in 2014, and I do not believe ... that deploying tens of thousands of British troops to fight the Taliban is an option."