OMG: Kurds War Against ISIS

But the YPG has been one of the most successful groups fighting ISIS, so now it's getting help from the U.S.-led coalition.

That's drawn the ire of Erdogan, 

who said last week the U.S. is responsible for a "sea of blood" in Syria because of its support for the YPG.

"YPG is part of the separatist terror organization," Davutoglu said on Thursday after the Ankara attack. "This was already known to us but we hope this act shows all our allies and the world this fact."