Britain's Defence Secretary has revealed his attempts to assemble a military coalition with Nato forces to keep troops in Afghanistan after the US announced its withdrawal.
Ben Wallace said he tried to convince "like-minded" countries to keep forces in Afghanistan alongside UK troops, but once his offer was rejected he decided the UK could not act alone.
"I did try talking to Nato nations but they were not interested, nearly all of them," Mr Wallace told the Daily Mail.
"We tried a number of like-minded nations. Some said they were keen but their parliaments weren't. It became apparent pretty quickly that without the United States as the framework nation it had been, these options were closed off.
"All of us were saddened, from the Prime Minister down, about all the blood and treasure that had been spent, that this was how it was ending."
US President Joe Biden has scheduled his country's military mission in Afghanistan to end on August 31.
He said the Afghan people must decide their own future and he will not consign another generation of American troops to the war that has already lasted 20 years.
Mr Wallace said last year's accord between former US president Donald Trump and the Taliban was a "rotten deal" and he expects Britain to return to Afghanistan, perhaps within a decade.
"It saddens me that the deal picked apart a lot of what had been achieved in Afghanistan over 20 years," he said.
"We’ll probably be back in 10 or 20 years. But acting now is not possible. The damage was done with the deal."
Britain's top genera, Sir Nick Carter, has called into question the legitimacy of the Taliban's actions.
"There is a big question about legitimacy and whether the west still wants to support Afghanistan if the Taliban have seized the country in a fashion that is quite obviously illegitimate," he told the BBC.
"Do the Taliban really want to become a pariah state again?"
On Monday, Taliban militants captured a sixth provincial capital, along with border towns and trade routes, and now control more than half the country.
US envoy for Afghanistan Zalmay Khalilzad is travelling to Qatar to "press the Taliban to stop their military offensive and to negotiate a political settlement", the State Department said on Monday.
Over three days, representatives from governments and multilateral organisations will press for "a reduction of violence and ceasefire and a commitment not to recognise a government imposed by force", it said.
The Taliban have stepped up their campaign to defeat government troops as foreign forces withdraw.
On Monday, they took Aybak, the capital of the northern province of Samangan.
It followed the capture at the weekend of Zaranj in the southern province of Nimruz, Sar-e-Pul in the northern province of the same name, and Taloqan, in north-eastern Takhar province.
The group has also taken the northern provincial capital of Kunduz and Lashkar Gah, capital of Helmand province.
Pentagon spokesman John Kirby said the US was deeply concerned about the trend but that Afghan security forces had the capability to fight against the insurgents.
"These are their military forces, these are their provincial capitals, their people to defend and it's really going to come down to the leadership that they're willing to exude here at this particular moment," he said.
He said there was "not much" the US military could do if Afghan security forces were not putting up a fight.
German Defence Minister Annegret Kramp-Karrenbauer has rejected calls for its soldiers to return to Afghanistan after the Taliban took Kunduz, where German troops were stationed for a decade.
Afghan commandos have launched a counterattack to try to beat back Taliban fighters who overran Kunduz.
In the West, near the border with Iran, security officials said heavy fighting was under way on the outskirts of Herat.
Arif Jalali, head of Herat Zonal Hospital, said 36 people were killed and 220 wounded in the past 11 days. More than half of those wounded were civilians.
The UN children's fund said 20 children were killed and 130 wounded in southern Kandahar province in the past 72 hours.
"The atrocities grow higher by the day," said Herve Ludovic De Lys, Unicef's representative in Afghanistan.