British forces could return to Afghanistan if al-Qaeda returns as the country teeters on the brink of civil war, the Defence Secretary has said.
The UK is sending 600 troops to evacuate British citizens and Afghan translators as the country plunged into further turmoil amid the withdrawal of allied forces.
The Taliban has swept through the country, seizing control of Kandahar, the second largest city, and a third of Afghanistan's regional capitals.
Ben Wallace expressed fears that al-Qaeda extremists could return, and did not rule out a mass deployment of British troops in Afghanistan.
Asked if the UK would send troops back to Afghanistan again, he told LBC: "I'm going to leave every option open.
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"If the Taliban have a message from last time, you start hosting al Qaeda, you start attacking the West, or countries like that, we could be back."
Pressed again, he said: "I’ll do whatever we need to do to defend the country. "
Mr Wallace expressed concern that Afghanistan would become a failed state, allowing militant groups like al-Qaeda to thrive.
He told Sky News: "Of course I am worried, it is why I said I felt this was not the right time or decision to make because, of course, Al-Qaeda will probably come back, certainly would like that type of breeding ground.
"That is what we see - failed states around the world lead to instability, lead to a security threat to us and our interests."
In another interview, he said: "Britain found that out in the 1830s, that it is a country led by warlords and led by different provinces and tribes, and you end up, if you're not very careful in a civil war, and I think we are heading towards a civil war."
Mr Wallace said former US President Donald Trump had made a "mistake" by making a deal with the Taliban to withdraw US forces - an agreement which has endured under Joe Biden.
He said: "I was public about it that at the time of the Trump deal - with obviously the Taliban - I felt that that was a mistake to have done it that way, that we will all, as an international community, pay the consequences of that.
"But when the United States, as the framework nation, took that decision, the way we were all configured, the way we had gone in meant that we had to leave as well."
Ex-Defence Minister Johnny Mercer, who served in Afghanistan, said it was "deeply humiliating" to watch events in the country and said the UK did not need to walk away.
He told BBC Breakfast: "Biden has made a huge mistake here, but also we have a role.
"This idea we cannot act unilaterally and support the Afghan security forces is simply not true.
"The political will to see through enduring support to Afghanistan has not been there and a lot of people are going to die because of that, and for me that is extremely humiliating.
"It's a world tragedy and we are going to reap the repercussions of this over many years to come."
Rory Stewart, a former Tory international development secretary, said: "This is a horrifying group associated with terrorists, they have been backing suicide bombing in the areas they control, women are not going to school and it is a total betrayal by the United States and the United Kingdom."
