A car bomb killed at least 53 people and wounded more than 200 in central Damascus on Thursday when it exploded on a busy highway close to ruling Baath Party offices and the Russian embassy, Syrian television said.

TV footage showed at least four charred and bloodied bodies strewn across the street after the blast, which state media said was the result of a suicide bombing by "terrorists" battling President Bashar al-Assad.

Central Damascus has been relatively insulated from almost two years of unrest and civil war in which around 70,000 people have been killed across the country, but the bloodshed has shattered suburbs around the capital.

Rebels who control districts to the south and east of Damascus have attacked Assad's power base for nearly a month and struck with devastating bombs over the last year.

The al Qaida-linked rebel group Jabhat al-Nusra, which claimed responsibility for several of those bombs, says it carried out 17 attacks around Damascus in the first half of February, including at least seven bombings.

The Syrian Observatory for Human Rights put the death toll from Thursday's attack in the Mazraa district of Damascus at 31, mostly civilians. Other activists said 40 people had died, including children from a nearby school.

Opposition activists reported further explosions elsewhere in the city after the mid-morning explosion in Mazraa.

One resident in the heart of the capital heard three or four projectiles whistling through the sky, followed by explosions.

At least one of them landed in a public garden in the Abu Rummaneh district, she said, but no one was hurt.

The Britain-based Observatory, which monitors violence via a network of sources inside Syria, said the Mazraa car bomb detonated at a checkpoint close to the Baath Party building, located about 200 meters (660 feet) from the Russian embassy.

Russia's Itar-Tass news agency quoted a diplomat as saying the blast blew out windows at the embassy but no employees were wounded. "The building has really been damaged ... The windows are shattered," the diplomat said.

The vehicle was carrying between 1 and 1.5 tons of explosives, Damascus Governor Bishr Sabban told Reuters.

A correspondent for Syrian television said he saw seven body bags with corpses at the scene. He counted 17 burnt-out cars and another 40 that were destroyed or badly damaged by the force of the blast, which ripped a crater 1.5 meters deep into the road.

The official SANA news agency said casualties included children at a nearby school in Mazraa, which it described as a busy residential district of the capital.

Later, the Observatory reported, two car bombs exploded outside security centers in the northeastern district of Barzeh, but there were no details of casualties.

Syrian TV said security forces detained a would-be suicide bomber with five bombs in his car, one of them weighing 300 kg.

Meanwhile, at least 18 people were killed Thursday in a bombardment by Syrian jet fighters of a field hospital in the restive southern province of Daraa, reported an opposition group. The dead included eight rebel fighters, three medics and seven civilians, added the Britain-based Syrian Observatory for Human Rights.-