Syria condemned on Sunday joint U.S.-Turkish patrols in a border strip in the northeast of the country, saying it was a "flagrant violation" of its sovereignty, an official statement said.
Armed Turkish military vehicles crossed into Syria on Sunday and headed southwest with their U.S. counterparts to begin planned joint patrols to establish a "safe zone" along a border region mainly controlled by Kurdish forces.
The move was also a violation of the "territorial integrity" of Syria, said the Syrian foreign ministry statement, referring to what the government considers attempts by the U.S.-backed Kurdish YPG militia to divide the country.
NATO allies, the U.S. and Turkey, have conducted multiple joint helicopter patrols over the area. Turkey, which hosts some 3.6 million Syrian refugees after eight years of war south of its border, hopes to resettle 1 million refugees in northern Syria.
"Our geography is an advantage, but we are at a disadvantage in terms of migration and terror," Turkish Interior Minister Suleyman Soylu said in a CNN Turk interview Sunday.
"If U.S. forces can patrol in the east of Euphrates with our forces and can enter with their own troops, and if there are the (Turkish) observation points in Idlib (in northwest Syria), this is all due to the steps taken by Turkey."
With U.S. backing over the last four years, the Syrian Democratic Forces (SDF) alliance that the YPG spearheads has taken control of much of northeastern Syria from Islamic State militants.
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Many of the inhabitants of the predominately Arab area that is expected to comprise the safe zone - including Tel Abyad, Ras al Ain and several Arab villages - had fled to Turkey fearing reprisals by the YPG on charges they had links to Islamic State