By Murad Sezer
AKCAKALE, Turkey (Reuters) - Armed Turkish military vehicles crossed into Syria on Sunday and headed southwest with U.S. counterparts to begin planned joint patrols to establish a "safe zone" along a border region mainly controlled by Kurdish forces.
Vehicles with Turkish flags joined those in Syria with U.S. flags some 15 kilometers (nine miles) east of the Turkish border town of Akcakale, near Syria's Tel Abyad. Two military helicopters were seen overhead.
The region east of the Euphrates river is mainly controlled by Kurdish YPG forces, U.S. allies that Ankara has labelled terrorists because it says they have links to Kurdish militants in Turkey.
After intensive negotiations, Turkey and the United States have also set up a joint operation centre but have so far disagreed over the zone's depth and over the command structure of the forces to operate there.
The NATO allies 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.
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.
(Reporting by Murad Sezer near Akcakale; Additional reporting by Irem Koca in Istanbul and Suleiman Al-Khalidi in Amman; Writing by Jonathan Spicer; editing by John Stonestreet)