At least 13 people were killed and dozens wounded when a Syrian mini-bus exploded Monday near the border between Turkey and Syria, officials said, though the cause was not immediately clear.

"All possibilities are on the table, including political motives," Deputy Prime Minister Bulent Arinc said after unidentified explosives triggered the "powerful blast".

The Syrian-registered mini-bus, which was travelling from the direction of Syria, exploded in a busy parking lot barely 40 metres (yards) into the buffer zone of the Cilvegozu crossing in the Turkish town of Reyhanli.

It sparked a fire that damaged about 15 vehicles, a foreign ministry official told AFP.

The official put the likelihood of it being a terrorist attack at "51 percent," but stressed the local prosecutor's office was still investigating.

"We have unfortunately lost 13 people: three of them Turks and rest Syrians," Prime Minister Recep Tayip Erdogan said, adding that another 27 people were severely wounded.

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.

Erdogan said the blast underscored why Turkey is prioritising counterterrorism efforts and maintaining a hard line against the regime of Syrian President Bashar al-Assad.

"We will not make concessions on either issue," he said.

Television footage showed smoke plumes rising from the parking lot and body parts could be seen scattered across the scene.

Another Turkish foreign ministry official said 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.

The Cilvegozu crossing is a major gateway used by hundreds of trucks, which form long lines every day to carry humanitarian aid into Syria.

"The area hit by the explosion is used for humanitarian aid organisations to switch their loads onto other vehicles," for distribution inside Syria, regional customs manager Adnan Korkmaz told the state-run Anatolia news agency.

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.

Turkey requested help from its NATO allies after the cross-border 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.

That blast was blamed on Kurdish rebels, who denied responsibility.

Turkey, a one-time Syria ally now vehemently opposed to 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.