Syrian Kurdish intelligence has warned that hundreds of Islamic State fighters from Britain are hiding in Turkey, adding to fears of an increased threat of attacks on European soil.

In an interview with The Times of London, Ciwan Xhalil, a Syrian Kurdish intelligence officer, who collaborates with western intelligence agencies over foreign Islamic State fighters, said most British fighters had fled Syria and gone to Turkey.

“The exodus began after Mosul [in Iraq] fell and continued after [Islamic State] lost Raqqa. We have lots of French in our jails and scores of other nationals but we think most of the British have escaped,” he said.

As reported by Newsweek online, British and European security services have long been worried about the exodus of foreign nationals from Iraq and Syria and their return to their home countries. Officials say the flow back to the continent has been slower than anticipated, but that does not mean they will not return eventually.

Around 900 British nationals travelled to Iraq and Syria to fight for Islamic State, according to estimates, but only half of those have returned. More than 100 were killed battling in the group’s ranks.

In a separate report, the Reuters news agency noted that fewer than 1,000 Islamic State fighters remain in Iraq and Syria. This is based on the United States-led international coalition fighting the hardline Sunni militant group.

“Due to the commitment of the Coalition and the demonstrated competence of our partners in Iraq and Syria, there are estimated to be less than 1,000 Islamic State terrorists in our combined joint area of operations, most of whom are being hunted down in the desert regions in eastern Syria and Western Iraq,” the US-led coalition told Reuters in an emailed statement.

The figure excludes areas in western Syria under the control of President Bashar al-Assad’s government and his allies.

Meanwhile, Assad’s main ally Russia also said on December 26 the main battle with Islamic State in Syria was over. Foreign Minister Sergei Lavrov said the key task in Syria was now destroying another Islamist group, the Nusra Front.

Earlier this month, the US-led coalition had said there were less than 3,000 fighters remaining. Iraq declared “final victory” over the group on December 9.