The British-based Syrian Observatory for Human Rights said the pipeline was "bombed," while the state-run news agency SANA blamed terrorists, but no casualties were reported and it was not clear who was behind the explosion.
"An armed terrorist group on Thursday committed an act of sabotage," SANA said.
A government official said the blast caused a fire that has been burning for four hours. The official spoke on condition of anonymity because he was not authorized to speak to the media.
The reports could not be independently confirmed.
Syria is trying to crush a 9-month-old uprising, but the conflict is turning more violent as once-peaceful protesters increasingly take up arms. Meanwhile, sanctions from Turkey, the Arab League and the European Union are aimed at squeezing the ailing Syrian economy and forcing the regime to halt the bloodshed.
The EU has banned oil imports from Syria in a move that costs the embattled regime millions of dollars each day.
On Wednesday, in a rare interview, Syrian President Bashar Assad said he never ordered the brutal suppression of the uprising in his country, and insisted only a "crazy person" would kill his own people.
Apparently trying to distance himself from violence that the U.N. says has killed 4,000 people since March, Assad laughed off a question in a rare interview broadcast Wednesday about whether he feels any guilt.
"I did my best to protect the people," he told ABC's Barbara Walters during an interview at the presidential palace in the Syrian capital, Damascus. "You feel sorry for the life that has been lost, but you don't feel guilty when you don't kill people."
"No government in the world (kills) its people unless it is led by a crazy person," Assad added in the interview, which was conducted in English. Assad, who trained as an ophthalmologist in Britain, speaks the language fluently.
The interview offered a rare glimpse into the character of the 46-year-old Assad, who inherited power from his father in 2000. His brother — widely regarded as the chosen heir — had died in a car crash years earlier.
Assad, who commands Syria's armed forces, has sealed off the country to most outsiders while clinging to the allegation that the uprising is the work of foreign extremists, not true reform-seekers aiming to open the authoritarian political system.
The United Nations and others dismiss that entirely, blaming the regime for widespread killings, rape and torture. Witnesses and activists inside Syria describe brutal repression, with government forces firing on unarmed protesters and conducting terrifying, house-to-house raids in which families are dragged from their homes in the night.
"We're talking about false allegations and accusations," Assad said. When asked if Syrian troops had cracked down too hard on protesters, he said there had been no command "to kill or to be brutal."
"They're not my forces," he said. "They are military forces (who) belong to the government. I don't own them. I'm president. I don't own the country."
Assad said some Syrian troops may have behaved badly, but they faced punishment if so. He also said most of the people who died in the unrest were his own supporters and troops, slain by terrorists and gangsters — an allegation disputed by most outside observers.