Turkish Prime Minister Recep Tayyip Erdogan said on Tuesday that a powerful blast in a minibus on the Syrian border which killed 14 people was a bomb attack.
"A vehicle loaded with bombs was able to reach our customs gate because the customs gate on the Syrian side is not working and is not being controlled," Erdogan told parliament after Monday's incident.
The vehicle exploded on Monday in the buffer zone between Turkey's Cilvegozu border crossing and Syria's Bab al-Hawa post, which was seized by Syrian rebels in July.
"What we see in the footage that it is a crowded parking lot filled with pedestrians... Anybody can see the death toll would be heavy," Justice Minister Sadullah Ergin told reporters earlier.
"So we believe civilians are the clear targets," Ergin added. "I curse this act of terror."
Turkish authorities are looking into all possibilities, including claims that the attack might have been carried out by Syrian intelligence, local media reported.
Dissident groups within the various factions of the Syrian rebels are also under the spotlight.
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The Cilvegozu crossing is one of seven functioning border posts along Turkey's 910 kilometre (560 mile) frontier with Syria.
It is a major gateway into Syria, with hundreds of trucks lining up every day to take humanitarian aid into the war-torn nation.
Video footage showed the minibus arriving from Syria and parking near the border crossing 20 minutes before it exploded, Interior Minister Muammer Guler said.
The Milliyet newspaper said around 50 kilogrammes (110) of TNT had been stashed in the vehicle and were detonated by remote control,
Officials put the toll at least 14, four of them Turks and the rest Syrians, while 25 others were wounded.
Hurriyet reported that three suspects got out of the car before the explosion. Two of them walked into Syria while the third entered Turkey and is still being hunted for.
Turkey, a one-time Syria ally now vehemently opposed to President Bashar al-Assad's regime, has taken in close to 200,000 refugees from the conflict that has killed more than 60,000 Syrians in nearly two years, according to UN figures.