Nine people were killed and dozens wounded when a car exploded on Monday near the border between Turkey and Syria, officials said, although the cause was not immediately clear.
A Syrian-registered car is believed to have been at the centre of the blast on Turkish soil, local mayor Huseyin Sanverdi told the NTV news channel.
Dozens of ambulances were dispatched to the scene at the Cilvegozu border crossing near the town of Reyhanli in the southern province of Hatay.
An official from the Turkish foreign ministry confirmed the deadly explosion, adding that the blast triggered a fire that damaged around 15 humanitarian aid vehicles.
The explosion happened barely 40 metres (yards) away from the Cilvegozu crossing, NTV reported, adding that it might have been caused by a mortar bomb fired from the Syrian side.
Another Turkish foreign ministry official said the explosion did not appear to have been caused by a mortar but that a suicide bomber might have been involved in the blast that smashed apart the gates at the crossing, opposite Syria's Bab al-Hawa post.
"It is too early to make a conclusion as the inquiry is still going on," the official told AFP on condition of anonymity.
The car was believed to have been parked at a crowded lot filled with trucks ready to leave for war-torn Syria with humanitarian supplies, the ministry official added.
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The explosion comes after a suicide bomber attacked the US embassy in Ankara on February 1, killing a Turkish security guard and wounding three others.
That attack was claimed by a radical Turkish Marxist group classified as a terrorist organisation by Turkey and the United States.
Monday's blast also came less than three weeks after NATO declared that a battery of US-made Patriot missiles had become operational on Turkey's border with Syria.
Several other batteries of the surface-to-air missiles have also been dispatched by NATO allies Germany and the Netherlands to protect Turkey from a possible spillover of the conflict in Syria.
Dozens of mortar shells have landed on Turkish soil in recent months, including a deadly incident in October when five Turkish civilians were killed by Syrian shelling.
Turkey requested help from its NATO allies after the shellings, which it reciprocated systematically by firing mortars into Syria.
In another deadly attack, a car bomb exploded near a police station in the southeastern city of Gaziantep in August, killing nine people, four of them children, and injuring dozens more. The blast was blamed on Kurdish rebels, who denied responsibility.
Turkey, a one-time Syria ally which is now vehemently opposed to President Bashar al-Assad's regime, has taken in close to 200,000 of refugees from the conflict which has killed more than 60,000 Syrians in nearly two years, according to UN figures.