An Islamist group not previously been known to be involved in Syria has claimed responsibility for two May 10 suicide bombings in Damascus that left 55 people dead.
The Al-Nusra Front issued a video saying that the bombings -- the single deadliest attack since the uprising against Syrian President Bashar al-Assad's regime started 14 months ago -- was in retaliation for government attacks on residential areas.
Little is known about Al-Nusra, although Western agencies believe it could be a front for a branch of Al-Qaeda based in Iraq.
The attack was the latest blow to a fragile cease-fire brokered in April by UN-Arab League envoy Kofi Annan.
The UN estimates more than 9,000 people have been killed since the uprising began in March 2011.
Meanwhile, an explosion was reported in the northern city of Aleppo.
Reports said no casualties were reported in the blast, which targeted a government building.
A guard, however, died in gunfire after the blast.
The bombing comes hours after Syrian officials said they had foiled a suicide bomb plot in the same city.
The state-run SANA news agency reported security forces had shot dead a suicide bomber before he was able to detonate 1,200 kilograms of explosives loaded into a van.
Based on reporting by Reuters and dpa