Bombs planted by rebels exploded at a school building occupied by security forces and pro-government militias in the Syrian capital of Damascus on Tuesday, activists and rebels said.
Residents said smoke was billowing from the area in southeastern Damascus and an activist said ambulances were rushing to the scene.
"At exactly 9:35 am, seven improvised devices were set off in two explosions to target a school used for weekly planning meetings between shabbiha militia and security officers," said Abu Moaz, a leader of Ansar al-Islam, one of the rebel groups in the 18-month-old revolt against President Bashar al-Assad.
The state news channel Syria TV quoted a government official as saying two improvised explosives planted by "terrorists" blew up near the "Sons of Martyrs" school in Damascus. It said seven people were wounded, with minor damage to buildings.
Rebels said they expected high casualties from the blast but they did not give any confirmed reports of deaths.
"There were several officers present, and we are hoping they will be part of a large number of killed in this operation," Abu Moaz said.
Southern Damascus has become a battleground between Assad's forces and opposition fighters. Last week, the army bombarded rebel strongholds there to flush them out of the capital, once seen as Assad's untouchable seat of power but now a site of daily fighting.
Damascus residents also reported heavy clashes for two hours on Baghdad Street in a central district of the capital just to the north of the Old City.