BEIRUT -- A deadly blast shook Damascus early Thursday, killing more than a dozen people, shattering windows and sending a cloud of smoke above the Syrian capital as emergency vehicles raced to the scene.
News reports indicated that the mid-morning explosion was probably a massive car bomb that detonated on busy Al Thawra Street in the Al Mazraa district in central Damascus, causing bloody mayhem in the heart of the city.
The official Syrian news agency reported that at least 16 civilians were killed and more than 200 injured, though the death toll seemed certain to rise, and news agencies reported at least 35 dead.
The victims were mostly pedestrians, schoolchildren and motorists, the state media said. The blast also damaged nearby Al Hayat Hospital and Abdullah Bin al-Zubir school, the official news agency reported.
After the explosion, there were reports of shells fired into the center of the capital, possibly aimed at military headquarters near Umayyad Square. Area residents abandoned the streets, and some took cover in basements. The government appeared to respond with artillery from positions on Mt. Qassion, which overlooks the capital.
Video broadcast on Syrian television showed hellish scenes of the bombing's aftermath.
Charred and burning vehicles were arrayed along a street strewn with mangled and burned bodies and body parts. Firefighters sought to douse lingering blazes, and rescue workers with stretchers struggled to evacuate the injured.
Several dazed survivors sat stunned along the roadside as fires raged in vehicles nearby. One man tried to revive a wounded person lying face-up on the road; another man seemed to be trying to crawl toward safety.
The bombing appeared to have heavily damaged a pedestrian overpass, along with at least one nearby multistory building that had its windows and window frames blown out. A photograph of a deep crater in the middle of the street may have indicated where the apparent car bomb detonated.
The official news agency also said an unexploded car bomb -- loaded with cylindrical water heaters filled with explosives -- had been seized at the scene. The "suicide terrorist" driving that vehicle was arrested, the state news agency said.
The blast comes as rebels based in the city's outskirts have stepped up attacks on the capital in an offensive that is now in its third week.
Rebels have used mortars and car bombs to press their assault, and have also attacked in force from various suburbs. The military, determined to stop any rebel advance on the capital, has responded with aerial bombardment and shelling of rebel strongholds outside the capital.
On Wednesday, the conflict that has convulsed Syria for almost two years reached the nation's sports fields. The state news agency reported that a professional soccer player was killed and several others were injured when a pair of mortar shells struck a sports complex in Damascus.
The dead player was identified as Youssef Suleiman, a member of the Al Wathba soccer team, based in the central city of Homs.
Reports indicated that Al Wathba players were preparing to go to a match against the Al Nawair team when the afternoon attack occurred, spraying players with shrapnel. Six other people suffered light injuries, reported the pro-government daily Al Watan.
The mortar shells struck the Tishreen Sports City, the official Syrian Arab News Agency reported.
The government media agency accused the opposition of "targeting sports cities and institutions," but vowed that players and teams would continue their training and matches.
Earlier this week, rebels announced a mortar attack on the Tishreen presidential palace. The government said no one was injured in that attack but that "terrorist" mortar shells caused minor damage to a pair of hospitals.
Also Wednesday, the opposition said a major rebel commander in the Damascus suburbs had been seriously injured in a government bombardment. There was no immediate word on the condition of the commander, identified as Sheikh Zahran Alloush, founder of the Liwa al-Islam brigade, which has been spearheading the insurgent offensive against the capital.
A special correspondent in Damascus contributed to this report.