An Islamic group blamed for a devastating twin car bombing that killed 55 people in Syria last week has denied responsibility for the attack.

Al-Nusra, a little known Islamic opposition group fighting Syrian President Bashar al-Assad, has denied a video released shortly after last Thursday's Damascus attack in which the group supposedly claimed responsibility was released by them.

Many news agencies, news websites, and satellite channels... have  attributed [the bombings] to Al-Nusra Front, based on a video posted on YouTube, said the statement dated May 13, Agence-France Presse reported.

But we say, this video as well as the statement appearing in it are fabricated and... full of errors.

We did not receive from the front's military department any affirmation or denial or information regarding the operation, the group said.

The group has however claimed responsibility for previous bombings, including double blasts in Damascus on March 17 that killed 27 people, as well as two other deadly explosions in the capital and two in the northern city of Aleppo, the AFP said.

Elsewhere, the Syrian National Council - a group of disparate opposition groups - voted to keep Burhan Ghalioun, 67, as their leader.

Ghalioun, a secular academic who has lived in France for several years, is seen as a shrewd choice to garner the support of foreign powers wary of backing the SNC.

The news follows the outbreak of violence in the Lebanese port city of Tripoli, leaving two dead and 20 injured, as tensions between supporters and opponents of the Assad regime spilled into the streets over the weekend.

The fighting, which first erupted on Saturday, was the worst violence in Lebanon, Syria's neighbor and historically close to Syrian politics, since the uprising against Assad began more than 14 months ago.

On Friday the Syrian government appealed to the United Nations for help in combating terrorism, saying that a spate of bombings prove that it is under attack from forces armed by foreign powers.

State media said Assad's regime called on the UN Security Council and secretary-general Ban Ki-moon for assistance in tackling the escalating crimes committed by what he called terrorists receiving help from abroad.