A mysterious blast ripped through a busy Turkish customs gate on the border with Syria on Monday, killing at least 13 people and wounding dozens, the Turkish government said.

Deputy Prime Minister Bulent Arinc, chief spokesman for the government, said a minivan traveling from Syria to Turkey exploded. He declined to call it a terrorist attack, saying the investigation was still ongoing.

"The type of explosive could not be determined as of this time," Arinc said.

"In situations like this all possibilities are considered."

There is no question, however, that this was one of the deadliest blasts to hit Turkey in years.

"It's like hell. People are injured," said a Turkish smuggler who asked to use only the name Gokmen because of the illicit nature of his work. He said he was on the Syrian side of the sprawling border terminal when he heard the blast.

Amateur video of the explosion aftermath showed bystanders running amid scattered shrapnel, burned-out cars and ambulances, screaming in panic and pain.

Bystanders carried a bleeding man from smoking wreckage near the traffic booths where Turkish border officials normally processed transiting cars and cargo trucks.

"My house is two kilometers (about a mile and a quarter) away from the border ... but the blast was powerful enough that we heard it," Mahmut Iri, the mayor of the Turkish border town of Cilvegozu, said in a phone call with CNN.

Iri said the explosion hit the last Turkish border gate before Syrian territory.

"I know for a fact that two of the people who died were Turks," Iri added.

Syrian rebels first overran the Syrian border gate at Bab el Hawa last summer, flushing out government forces after days of fighting.

Within several months, Turkey was allowing vehicles through the border gate to rebel-controlled Syria.

Turkish officials have not yet commented on the cause of the deadly blast.

Over the past 22 months, fighting has frequently spilled over Turkey's 900-kilometer (560-mile) border with Syria.

In October, five Turkish civilians were killed when Syrian troops shelled the Turkish border town of Akcakale. And in June, Syrian anti-aircraft fire brought down a Turkish military reconnaissance jet over the Mediterranean Sea.

When fighting erupts across the border, Turkish authorities periodically close schools that are close to Turkish territory.

In recent months, the NATO military alliance has responded to a Turkish government request for assistance by deploying Patriot missile batteries around major cities close to the Syrian border. Hundreds of American, German and Dutch troops have been sent to Turkey to operate the Patriots, which the Turkish government says are designed to protect Turkey from the threat of Syrian ballistic missiles.

On Feb. 1, a suicide bomber attacked the entrance to the U.S. Embassy in Turkey's capital, Ankara, killing a Turkish guard and seriously wounding a Turkish journalist. A violent leftist group called the Revolutionary People's Liberation Party-Front, or DHKP-C, claimed responsibility for the attack.

In a rambling online manifesto, the group said one of the reasons the U.S. Embassy was targeted was to stop what it called American imperialist plans to colonize Syria and Turkey.

Fighting inside Syria

Meanwhile, Syrian rebels claimed to have captured Syria's largest man-made dam on Monday.

"The Free Army took control of the city of Tabqa and the Euphrates (Tabqa) Dam," the opposition Media Center in Tabqa announced in an online posting.

"If clashes will happen, this will cause big damage and the whole area will drown and many places will lose electricity."

CNN could not independently confirm claims that the dam had been captured. The Syrian government did not respond to opposition claims that its forces had lost control of the dam.