US President Donald Trump said that two Britons, who are accused of being part of an Islamic State (IS) terror group cell which kidnapped and murdered Western hostages, have been taken out of Syria to “a secure location controlled” by Washington, according to reports on Tuesday.

Taking to Twitter on Wednesday, Trump said, “In case the Kurds or Turkey lose control, the US has already taken the two IS militants tied to beheadings in Syria, known as the Beetles (actual spelling Beatles), out of that country and into a secure location controlled by the US. They are the worst of the worst.”

El Shafee Elsheikh and Alexanda Kotey, who are from London, are in the custody of the American military, the BBC reported.

Trump’s announcement comes after the US withdrew its forces from the region this week.

Trump said that he had spoken to Boris Johnson on the subject of ISIS prisoners, but did not say whether he was referring to Kotey and Elsheikh. It is not clear how many prisoners are involved in the transfer.

The duo were part of a group of four who are accused of being involved in the apparently filmed beheadings of British aid workers David Haines and Alan Henning and American journalists James Foley and Steven Sotloff.

Earlier on Wednesday, President Trump said while speaking to media that the US had transferred “some of the most dangerous IS fighters” amid fears they could escape custody as Turkish troops invade Kurdish-held territory in northern Syria.

The Kurds, who helped defeat the terror group in Syria and were key US allies in that fight, guard thousands of IS fighters and their relatives in prisons and camps in areas under their control.

It was unclear whether they would continue to do so if fighting breaks out.