A British man was among two suspected ISIS fighters seized by the Taliban at a border crossing in northern Afghanistan, according to a report.
The pair had tried to slip into the country in the town of Hairatan, which straddles Uzbekistan and Afghanistan.
One was carrying a British passport, while the other had documents from another European country, a Taliban source told The Guardian.
He said the men were carrying more than £10,000 in cash, military fatigues and night-vision goggles in their bags.
Members of the Taliban arrested them after a tip-off from Uzbek authorities.
“There was one passport from England and one from another country in Europe,” said the source.
An Uzbek source said both men had been using British passports when they flew into the capital, Tashkent, and both had Afghan heritage. It is not clear if one of the men had been carrying two passports.
Britain’s Foreign and Commonwealth Office declined to comment.
ISIS’s affiliate in Afghanistan, known as ISIS-K, is the most extreme and violent militant group in the landlocked country. In August the group claimed responsibility for a suicide bombing outside Kabul Airport that killed 170 Afghan civilians and 13 US military personnel who had been involved in evacuation efforts.
After the Taliban regained control of Afghanistan in August there were fears that the country would once again become a safe haven for international terrorist groups. Taliban leaders have vowed not to shelter terrorists.
After war broke out in Syria in 2011, ISIS established themselves and deemed the northern city of Raqqa the capital of their caliphate.
Hundreds of British men and women travelled to the country to live under the terrorist group.
While authorities in the UK have for years been dealing with cases involving British citizens travelling to and returning from ISIS-controlled territory, this is the first reported case of a Briton attempting to join ISIS-K since the Taliban took over Afghanistan.
ISIS-K ranks are believed to have swelled to around 3,000 fighters at one time. However, the group suffered significant losses in clashes with both American and Afghan security forces, and also with the Taliban.
The group has attacked Afghan security forces, Afghan politicians and ministries, religious minorities, US and Nato forces, and the Taliban. International agencies and charities working in Afghanistan have also suffered at the hands of ISIS-K fighters.