The Turkish president, Recep Tayyip Erdoğan, has issued a thinly veiled threat that Turkey could release jailed Islamic State fighters and send them to Europe, a day after the country began its controversial policy of deporting foreign jihadists in its custody.

“You should revise your stance towards Turkey, which at the moment holds so many Isis members in prison and at the same time controls those in Syria,” Erdoğan told European countries in remarks to reporters in Ankara on Tuesday.

“These gates will open and these Isis members who have started to be sent to you will continue to be sent. Then you can take care of your own problem.”