A powerful car bomb exploded near the ruling Baath party headquarters in the Syrian capital on Thursday, killing at least 31 people, wounding dozens and leaving a trail of destruction, a watchdog said.
"At least 31 people were killed and dozens wounded, the majority civilians," said the Syrian Observatory for Human Rights, while the state news agency SANA reported 16 killed and 200 hurt in what it said was a suicide bombing.
Shortly after the mid-morning blast, two mortars were fired at a military headquarters in Damascus, Al-Ekhbariya and the Observatory both reported, without giving information on casualties.
The car bomb exploded at the 16 November Square near the Al-Iman mosque, next to the head offices of the Baath party, which has been in power for half a century.
Buildings were shattered by the blast, which sent thick black smoke billowing across the capital's skyline and all roads in the area were quickly sealed off, an AFP correspondent said.
Ambulances sirens rang out, and machinegun fire was also heard in the area, as firemen rushed to the scene to douse the flames.
There was no immediate claim of responsibility for the attack, which left a large crater in a major road, according to pictures released by the SANA state news agency.
"It is terrorism... Is that what you call Islam?" one of the wounded told Syrian television.
"Is that the freedom you want? Is that the (rebel) Free Syrian Army?" said another man, speaking at the site of the attack.
The windows of the Russian embassy were blown out by the blast, but none of its staff were hurt, Russian news agencies reported.
Moscow is one of the few big powers to keep ties with the regime of Syrian President Bashar al-Assad amid the conflict with rebels and retains a diplomatic presence in the Syrian capital.
According to the Observatory, which relies on a network of sources on the ground for its information, two other car bombs exploded next to security posts in the Barzeh district of north Damascus.
The General Staff building that came under mortar fire on Thursday lies next to the heavily fortified Omeyyades Square, in a district housing numerous government buildings. It was targeted in an attack last September that left four people dead.
There have been numerous deadly attacks on official targets in the Syrian capital in recent months, among them government, intelligence and security buildings.
The last car bombing in Damascus took place on January 4, killing 11 people, including children.
Protests against Assad's rule broke out in March 2011 but later morphed into an insurgency after the embattled president's forces unleashed a brutal crackdown on dissent.
The United Nations says at least 70,000 people have been killed in the conflict, and puts the number of Syrians who have fled their homeland at more than 850,000.