(CNN) -- A car bomb targeting the headquarters of Syria's ruling party killed 53 people in central Damascus Thursday, opposition activists and state-run media said.

The explosion was also close to a Russian Embassy building complex, but no one there was killed, that country's Foreign Ministry said.

Most of the dead were civilians. It's unclear who is behind the blast.

The explosion wounded more than 230 more people and burned 17 cars, Syrian state TV said.

Ambulances raced to the scene as body bags were brought for the charred remains of passengers who were in a taxi, according to state television.

The bomb detonated at a checkpoint manned by government soldiers in front of the Baath Socialist Party's main office, the Syrian Observatory for Human Rights said. The neighborhood is also home to Iraqi refugees, as well as Druze and Christian groups.

It was unclear whether the driver blew up the car while sitting inside it, or parked the vehicle and left before setting it off.

The main Syrian opposition, the National Coalition for the Revolutionary and Opposition Forces, posted a statement on Facebook saying President Bashar al-Assad's government was guilty of shelling residential neighborhoods and other crimes.

The "terrorist Assad regime" wishes to push Syrians "to the brink of despair," it said.

The car bomb exploded just 65 feet away from the Baath Party building and damaged it, a resident named Mohammed told CNN. Two schools are close by, and teachers phoned parents, asking them to pick up their children, he said. He did not want to give his last name because he was concerned for his own safety.

There was damage as far away as 1,000 feet (305 meters), the Syrian Observatory for Human Rights reported.

In a separate incident, two car bombs exploded at government checkpoints in the Damascus suburb of Barzeh. Clashes ensued after the explosions, the Observatory said.

In addition, two mortar rounds struck the Damascus offices of the Syrian army's leadership, the opposition reported.

In early January, a car bomb demolished a gas station close to a hospital in Barzeh, killing civilians. The government and opposition groups blamed each other for the attack.

Over the last year, rebels fighting to topple al-Assad's government have made inroads in the Damascus suburbs and have conducted potent strikes against government targets in the capital.

Syrian government forces continued heavy aerial bombardments over rebel strongholds Thursday. Multiple attacks targeted towns in Idlib province in the north and in Daraa province bordering Israel, Jordan and Lebanon.

The United Nations says about 70,000 people have been killed in Syria's civil war, which began nearly two years ago.

CNN's Ivan Watson contributed to this report.