A blast ripped through a bus carrying Lebanese Shia pilgrims in Damascus on Sunday, killing at least seven people, a monitor said, in an attack claimed by al-Qaeda's Syrian branch.

The Syrian Observatory for Human Rights said at least 20 people were wounded in the explosion near Souq al-Hamadiyeh district, and that six of the dead were Lebanese citizens.

The Lebanese agency that organised their trip gave the same death toll. Syrian state media said the blast was caused by an explosive device rather than by a suicide bomber.

Officials had found and defused a second bomb that had been placed inside the bus before it detonated, said the official SANA news agency.

Al-Nusra Front, the affiliate of al-Qaeda in Syria, claimed responsibility for the attack in a statement posted online.

The pilgrims were on a tour of religious sites.The bus had made its first stop at the Sayyida Roqaya shrine and was heading towards the revered Sayyida Zeinab shrine in southeast Damascus when the attack occurred.

Syrian state television showed footage from the scene of the blast, with men in military uniforms picking through the wreckage of the bus.

Its front half was mostly blown off, leaving only the metal frame, and bags of belongings were strewn across the remaining seats.

The Lebanese Shia movement Hezbollah denounced the attack. This "is part of the series of explosions that targets pilgrims in Syria, civilians in Iraq, believers in Pakistan" and "proves the barbarity of the terrorists", it said in a statement.

Parts of Damascus have remained relatively unscathed by the fighting raging in much of Syria since the beginning of the war, but rebels regularly fire rockets into the capital from rear bases in the surrounding countryside and the city has also been hit by bombings.

'Flush out all terrorists'

Earlier on Sunday Syria's prime minister Wael al-Halqi told parliament that the country's main aim was to "flush out all terrorists from its land" this year.

He said Syria would not allow its enemies "to destroy the land of religions and cradle of civilisations" and praised the army for its efforts.

Syria's uprising started in March 2011 with anti-government protests and has descended into a civil war pitting a range of rebel groups against the military.

More than 200,000 people were killed since the war broke out. The conflict erupted when security forces cracked down on protesters, sparking an uprising against President Bashar al-Assad's regime that escalated into full blown civil war.

At least three million refugees are registered refugees in neighbouring countries, in what the UN calls the biggest humanitarian emergency of our era.

Source: Agencies