Witnesses said they saw the vehicle drive up to the Cilvegözü border post, one of the main crossing points for Syrian refugees into Turkey, shortly before the explosion.
In the first official comment on the explosion, Deputy Prime Minister Bülent Arınç said the government is investigating all possible causes for the blast, including a suicide attack, but it is 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," Arınç, who is also the government spokesman, told reporters 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," he said.
Officials later on the day said death toll from the blast had risen to 13, including three Turks. At least 28 people were wounded, 13 of them seriously.
The minibus exploded as it was driving through a stretch of no-man's land between the two countries only metres (yards) away from the Turkish border gate, where scores of Syrian civilians and Turkish humanitarian workers were congregated, Arınç said.
He also said office of Reyhanlı Prosecutor launched an investigation over the blast and intelligence agencies are working to sort out the incident.
Speaking at a dinner attended by all ambassadors of EU countries and held at the Prime Ministry in Ankara on Monday, Prime Minister Erdoğan said the incident is of critical importance for showing how Turkey is right regarding its sensitivity about terrorism and the ongoing conflict in Syria, as well as Ankara's efforts.
With regard to fighting terrorism and its approach towards the events taking place in Syria, Erdoğan said Turkey will make no concession to its stance and will maintain its determination, in what seemed to be an open reference to comments that appeared in Turkish media suggesting that the blast could be a signal from Damascus.
Speaking from the scene of the blast, 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.
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.
Justice Minister Sadullah Ergin, Customs and Trade Minister Hayati Yazıcı and Interior Minister Muammer Güler went to the region late on Monday.
Local officials briefed the ministers about the situation. The three ministers paid a visit to Reyhanlı State Hospital, where the injured are receiving medical treatment.
After completion their visit, the minister left Hatay without holding a press conference.
Earlier reports had said a mortar round landed in the area but an official said the powerful blast did not look like a mortar attack. “There was an explosion in the no-man's zone. It was not a mortar attack. It was very strong," a foreign ministry spokesman told Reuters.
The circumstances of the explosion were not immediately clear, with earlier reports suggesting a mortar attack or accidental explosion of inflammable materials on the vehicle. “We don't know whether this was a suicide bomb or whether a car that was smuggling petrol across the border blew up," an official speaking on condition of anonymity told Reuters.
Hasan Akgöl, a lawmaker from the opposition Republican People's Party (CHP), however, said after visiting the scene of the explosion that the incident looked like a suicide attack, dismissing reports that the vehicle was carrying bottled gas that might have accidentally exploded. “But we cannot know exactly before security camera footage is examined,” he told private broadcaster NTV. Reports said that there might have been liquefied petroleum gas on the vehicle to increase the intensity of the explosion.
He also said the death toll appeared to be more than 10. “Bodies were on the ground,” he said.
Television footage and photographs showed severe damage to a series of cars at the border, where a gate was blown open and part of the roof collapsed. The area where the explosion took place was a transfer hub for aid materials sent to Syria, head of the Eastern Mediterranean Customs and Trade Directorate Adnan Korkmaz told the Anatolia news agency.
Interior Minister Muammer Güler was constantly in touch with Prime Minister Erdoğan, who was attending a weekly Cabinet meeting when the explosion took place.
The Cilvegözü border gate, several kilometers outside the town of Reyhanlı, sits opposite the Syrian gate of Bab al-Hawa, which the opposition forces captured last July. Refugees cross back and forth and Turkish trucks also deliver goods into no-man's land between the two gates, where they are picked up by Syrians.
Turkey is a staunch supporter of the nearly 2-year-old uprising against Syrian President Bashar al-Assad and has harbored both Syrian refugees and opposition fighters.
In October, Turkey hit targets inside Syria after a mortar bomb fired from Syria landed in a house in the border town of Akçakale, killing five Turks.