Two suicide car bombs ripped through the Syrian capital, killing 55 people and tearing the facade off a military intelligence building in the deadliest explosions since the country's uprising began 14 months ago.
Residents said the blasts happened in quick succession during morning rush hour, with an initial small explosion followed by a larger bomb that appeared aimed at onlookers and rescue crews arriving at the scene.
There was no claim of responsibility but an al Qaida-inspired group has claimed responsibility for several past explosions, raising fears that terrorist groups are entering the fray and exploiting the chaos.
More than 370 people were wounded. in the attack. The explosives weighed more than 1,000 kilos (2,200 lbs).
The US condemned the attack, with State Department spokeswoman Victoria Nuland saying "any and all violence that results in the indiscriminate killing and injury of civilians is reprehensible and cannot be justified."
Central Damascus is under the tight control of forces loyal to President Bashar Assad but has been struck by several bomb attacks, often targeting security installations or convoys, since the revolt against him began in March 2011.
The new blasts were similar to attacks waged by al Qaida in Iraq, which would bolster past allegations by top US intelligence officials that the terror network from the neighbouring country was the likely culprit behind previous bombings in Syria. That raises the possibility that its fighters are infiltrating across the border to take advantage of the political turmoil.
The Syrian government blames the bombings on the terrorists it says are behind the uprising, which has been the most potent challenge to the Assad family dynasty in Syria in four decades. But opposition leaders and activists routinely blame the regime for orchestrating the attacks.
Maj Gen Robert Mood, the Norwegian head of the UN's ceasefire monitors in the country, toured the site and said the Syrian people do not deserve this "terrible violence."
The relentless violence in the country has brought a ceasefire plan brokered by special envoy Kofi Annan to the brink of collapse. The UN said weeks ago that more than 9,000 people had been killed. Hundreds more have died since. Mr Annan appealed for calm and an end to bloodshed. "The Syrian people have already suffered too much," he said in a statement.