Turkish President Recep Tayyip Erdogan on Tuesday issued a chilling threat to Europe over looming sanctions over Ankara's unauthorized drilling in the Mediterranean: penalize us and we'll release ISIS prisoners back to European countries.

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"You should revise your stance toward Turkey, which holds so many IS members in prison and controls them in Syria," he told reporters.

The Associated Press reported that his comments were in response to the European Union’s unveiling of a system for imposing sanctions on Turkey over drilling off Cyprus. He made the comments while speaking to reporters prior to a trip to the U.S. to meet with President Trump.

Erdogan also said Turkey would continue repatriating foreign Islamic State militants to their home countries, even if these countries decline to take them back.

His move to use ISIS prisoners as a bargaining chip is a troubling turn. Turkey's motivation for the offensive has been debated and Ankara has been accused of poor planning and security standards at these so-called prisons.

Early in the invasion, more than 100 ISIS fighters who were being held in Kurdish prisons in the country are now on the loose in the days after the invasion.

Trump gave Ankara a green light for an offensive in Syria last month. The decision sent shockwaves through the region and Washington, with U.S. officials telling Fox News that top Pentagon officials were “completely blindsided” and “shocked” by the order to pull back hundreds of U.S. troops, a move that effectively green-lights the Turkey operation.

Sen. Chuck Schumer, D-N.Y., took to Twitter last week to criticize Trump for rolling out the welcome mat for Erdogan, "an autocrat whose actions threaten our allies & partners."

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“You still haven’t told us your plan to contain ISIS prisoners who escaped a fter Erdogan’s invasion of northern Syria!” he wrote.

Fox News' Greg Norman and the Associated Press contributed to this report