At least 14 people have been killed and 26 others wounded following a car-bomb explosion near the border between Turkey and Syria, according to the Turkish ministry of justice.
Witnesses said on Monday they saw the vehicle drive up to the Cilvegozu border post, one of the main crossing points for Syrian refugees into Turkey, shortly before the explosion.
The Cilvegozu border gate, several miles outside the town of Reyhanli, sits opposite the Syrian gate of Bab al-Hawa, which the rebels captured last July.
Refugees cross back and forth and Turkish lorries also deliver goods into no-man's land between the two gates, where they are picked up by Syrians.
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Bulent Arinc, deputy prime minister, said the Turkish government was investigating all possible causes for the blast, including a suicide attack, but it was wrong to jump to hasty conclusions.
"The information that we have for now is that a minibus with Syrian number plates coming form the other side exploded. It was a powerful explosion," Arinc, who is also the government spokesman, said after a regular cabinet meeting.
"But whether this was a vehicle laden with explosives or another type of explosion, I think, at the latest, will become clear tomorrow."
Turkey's interior, justice and customs ministers were due to fly to the area later on Monday to be briefed on the incident.
The justice ministry said four of the dead were Turks and eight of the injured were seriously wounded.
The minibus exploded as it was driving through a stretch of no-man's land between the two countries only metres away from the Turkish border gate, where scores of Syrian civilians and Turkish humanitarian workers were congregated, Arinc said.
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.
In October, five Turkish civilians were killed when a mortar shell hit a house in the Turkish border town of Akcakale.
Turkey has always responded to cross-border gunfire and mortar rounds, and is currently hosting NATO Patriot missile batteries to defend against attacks from Syria.