Witnesses said they saw the car drive up to the Cilvegozu border post, one of the main crossing points for Syrian refugees into Turkey, shortly before the explosion.
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"We don't know whether this was a suicide bomb or whether a car that was smuggling petrol across the border blew up," one Turkish official told Reuters.
The mayor of Reyhanli told CNN Turk that nine people were killed, four of them Turkish, and that the car which exploded had Syrian license plates.
Scene of the attack at the Syrian-Turkish border (Photo: Reuters)
Television footage and photographs showed severe damage to a series of vehicles at the border, where a gate was blown open and part of the roof collapsed.
Turkey is a staunch supporter of the near two-year uprising against Syrian President Bashar Assad and has harbored both Syrian refugees and rebels. Violence has sometimes spilled over the border.
Speaking from scene, Syrian opposition campaigner Osama Semaan said he believed the explosion was an attack by Assad loyalists in response to an offer of talks from opposition Syrian National Coalition
leader Moaz Alkhatib.
"It seems it is a deadly message from the Syrian regime after Sheikh Moaz offered it to talk in northern Syria," Seeman said.
Alkhatib said on Sunday he was willing to hold talks with Assad's representatives in rebel-held areas of northern Syria to try to end a conflict that has killed some 60,000 people.
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