Turkish tanks rolled into northern Syria on Wednesday as part of an offensive aimed at securing the border town of Jarablus from both Islamic State militants and Syrian Kurdish rebels.
The tanks were part of an unprecedented coalition that included Turkish-backed Syrian rebels and American and Turkish aircraft. Turkish special forces and artillery also took part in the operation.
"This morning at 4:00am, an operation started in northern Syria against terror groups which constantly threaten our country, like Daesh (Islamic State) and the PYD," Turkish President Tayip Erdogan said in a speech in Ankara.
Explosions echoed across the Turkish border as Turkish artillery and rocket fire destroyed 70 targets in the Jarablus area, and airstrikes hit another 12 targets, Turkish media reported. Turkish military officials said the airstrikes and artillery were being used to open up a passage for the ground troops.
Jarablus is one of the last remaining Islamic State-held towns on the Syrian-Turkish border, and serves as a key supply route for the militant group.
Meanwhile, Syrian Kurdish PYD guerrillas have expanded their territory in northern Syria by ousting Islamic State from towns and then occupying them, and the Turkish offensive appears to be an attempt to preempt the Kurds from doing the same in Jarablus. Turkey has declared the Euphrates river a red line that the Kurds should not cross, and Jarablus lies just to the west of the river.
Foreign Minister Mevlut Cavusoglu warned that Turkey would "do what is necessary" if Kurdish fighters didn't stay east of the river, Reuters reported.
Ankara sees the Syrian Kurdish rebels as an extension of the Kurdish insurgency on its own soil, and fears that if Syria's Kurds continue to expand their already semi-autonomous zone along the border, it could inspire Kurds to attempt to do the same in Turkey.
Redur Xelil, a spokesman for the Syrian Kurdish YPG militia, told Reuters that Turkey's offensive was a "blatant aggression in Syrian internal affairs."
While the US is allied with the PYD and other Syrian Kurdish groups against Islamic State, the US and Turkey share the goal of driving IS from the border, which the violent Islamist militant group has used to resupply its forces, make money from smuggling, and to replenish its ranks of foreign fighters.
The offensive against Jarablus comes after several attacks claimed by Islamic State targeted tourists and other civilians in Turkey, including a suicide bombing at a Kurdish wedding on Saturday that killed 54 of people in the southern Turkish city of Gazientep.
Reports suggested that as many as 1500 Turkish-backed syrian rebels were participating in the offensive.
US Vice President Joe Biden arrived in Ankara on Wednesday, the most senior US official to visit the NATO member since a coup attempt in July by a renegade wing of the military.
A senior US official traveling with Biden told Reuters that the US has provided air cover to the Turkish Operation, dubbed "Euphrates Shield," and will help Turkey push Islamic State back from the border.
The official said the US is "syncing up" with the Turks on their plans for Jarablus after Islamic State leaves, and that Turkish shelling was hitting Islamic State, not Kurdish forces.
Turkey shelled the Kurdish PYD militiamen in the town of Manbij on Monday, before the offensive began, which puts the US in an awkward position: The US has worked closely with the Kurds over the past months to drive Islamic State from Manbij.
Biden is expected to meet with Turkish President Rayep Erdogan to discuss US and Turkish objectives in Syria, and to also address Turkish demands that the US extradite a Turkish cleric who is in exile in the United States and who Erdogan says is the orchestrator of the attempted coup.
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