“We have thousands of Isis fighters that we want Europe to take and let’s see if they take them. And if they don’t take them, we’ll probably have to release them to Europe,” Mr Trump said on the White House lawn on Thursday.

The SDF is thought to be holding around 13,000 foreigners suspected of Isis links — not including Iraqi or Syrian fighters. That number is made up of 2,000 men and 11,000 women and children, most of whom were detained when the terror group’s caliphate fell earlier this year.