Turkey will send captured Islamic State members back to their countries even if their citizenships have been revoked, Interior Minister Suleyman Soylu says, criticising the approach of European countries on the issue.

The country launched an offensive into northeastern Syria against the Kurdish YPG militia last month following a decision by US President Donald Trump to withdraw troops from the region.

The move prompted widespread concern over the fate of Islamic State prisoners in the region.

AP

The YPG is the main element of the Syrian Democratic Forces (SDF), which has been a leading US ally in beating back Islamic State in the region, and has kept thousands of jihadists in jails across northeastern Syria.

The United States and Turkey's Western allies have said Turkey's offensive could hinder the fight against Islamic State and aid its resurgence.

Turkey, which views the YPG as a terrorist group linked with insurgent Kurdish militants on its own soil, has rejected those concerns and vowed to combat Islamic State with its allies. It has repeatedly called on European countries to take back their citizens fighting for the jihadists.

Speaking to reporters, Mr Soylu said Turkey would send back any captured Islamic State fighters to their countries even if their citizenships are revoked.

"We will send back those in our hands, but the world has come up with a new method now: revoking their citizenships," Mr Soylu said.

"They are saying they should be tried where they have been caught. This is a new form of international law, I guess ... It is not possible to accept this. We will send back Daesh [Islamic State] members in our hands to their own countries whether they revoke their citizenships or not."

Mr Soylu had warned at the weekend that Turkey would send back Islamic State members captured by Turkey to their home countries and complained of European inaction on the matter.