Alleged car bomb blast hits Damascus, Syria, near Bashar Assad's Baath party HQ, Russian Embassy

Updated at 10:52 a.m. Eastern

DAMASCUS, Syria A car bomb shook central Damascus on Thursday, exploding near the headquarters of the ruling Baath party and the Russian Embassy and killing dozens of people, officials and opposition activists said.

Syrian state TV reported the blast in the central Mazraa neighborhood, calling it a "terrorist" attack.

CBS News' George Baghdadi said Syrian officials estimated at least 53 people were killed in the blast, according to Syrian State TV, and another 200 injured. Syrian media said the explosion was near the Abdullah Bin al-Zubeir school, and many students were among the victims. Anti-regime activists put the death toll at 59.

Officials reported the blast was the result of a suicide car bomber. One Syrian source told Baghdadi a second car wired up with explosives was found at the scene but did not detonate. That claim could not immediately be verified, but if there was a secondary device set to explode with or after the initial bomb, it could suggest involvement by a salafist Islamic militant group. It is a tactic often used by groups which share motives, and in some cases links, to al Qaeda.

"It was huge. Everything in the shop turned upside down,'' one local resident said. He said three of his employees were injured by flying glass that killed a young girl who was walking by when the blast hit.

"I pulled her inside the shop but she was almost gone. We couldn't save her. She was hit in the stomach and head,'' he said, speaking on condition of anonymity for fear of retribution for speaking with foreign media.

Some of the most effective rebel groups battling to topple Assad's regime are salafist, including the al Nusra Brigades, which is believed to include former al Qaeda in Iraq fighters from across the border. Several large bombings in Damascus have been blamed on the group.

Baghdadi said the explosion caused huge damage in the neighborhood, with many cars left charred. Baghdadi said the sound of ambulance sirens wailing as they came to and from the scene continued unabated.

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The explosion shattered windows and sent up a huge cloud of smoke visible throughout much of the city. Reports said a car exploded at a security checkpoint between the Russian Embassy and the central headquarters of the ruling Baath party of President Bashar Assad.

An opposition group said, meanwhile, that 18 people were killed in a government air strike on a rebel field hospital in the southern city of Daraa, where Syria's uprising began nearly two years ago.

The Britain-based activist group the Syrian Observatory for Human Rights said those killed in the strike included eight rebel fighters, three medics, one woman and one young girl.

They Syrian capital has so far mostly avoided the large scale violence that has destroyed other Syrian cities, though deadly car bombings have targeted government buildings before.

Rebels have also targeted various government buildings with sporadic mortar fire this week, with two more landing near the army headquarters in Damascus on Thursday, reportedly causing no injuries. The army's headquarters, which is still being repaired from a bomb attack last year, is only about one mile from the scene of Thursday's car bombing.