DAMASCUS, Syria (AP) -- A car bomb exploded at a security checkpoint near the headquarters of the ruling Baath party in the heart of the Syrian capital on Thursday, leaving smashed cars scattered across a main thoroughfare and killing at least 31 people, according to opposition activist and state media. The bomb attack came amid a string of attacks inside the capital. A blast shook another Damascus neighborhood Thursday and mortars rounds fell near the Syrian Army General Command, the third such attack in Damascus in as many days. For months, rebels have been trying to bring their fight to topple President Bashar Assad into the capital, but have managed little more than brief incursions and frequent skirmishes in outlying neighborhoods. The latest bombings and the recent mortar attacks suggest they may be shifting to guerrilla tactics to destabilize the seat of Assad's power. The most deadly attack struck a main street on the edge of the capital's central Mazraa neighborhood, near the headquarters of Assad's Baath party and the Russian Embassy, as well as a mosque, a hospital and a school. TV footage of the blast site showed firemen dousing a flaming car with hoses and lifeless and dismembered bodies blown into the grass of a nearby park. Witnesses at the scene said a car had exploded at a security checkpoint between the Russian Embassy and the central headquarters of the ruling party. "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.