Alexanda Kotey and El Shafee Elsheikh, were members of a British group of Isis militants known as “the Beatles” and are understood to be amongst a number of fighters in the process of being transferred to the Americans.

US officials briefed media on the custody operation overnight, with the action first reported by the Washington Post. Prisoners previously held by the Syrian Kurds were first expected to be taken to neighbouring Iraq.

Donald Trump said: “We have taken a certain number of Isis fighters that are particularly bad, and we’ve wanted to make sure that nothing happened with them with respect to getting out.”

The US president subsequently tweeted: “In case the Kurds or Turkey lose control, the United States has already taken the 2 ISIS militants tied to beheadings in Syria, known as the Beetles, out of that country and into a secure location controlled by the U.S. They are the worst of the worst!”