BEIRUT — Activists say Syrian troops have shelled southern neighborhoods of the capital as they try to advance in rebel-held areas.

The Britain-based Syrian Observatory for Human Rights says the shelling of Tadamon and Hajar Aswad came as government troops conducted raids in the central Damascus neighborhood of Bab Sreijeh.

The violence came as Iran's parliament speaker Ali Larijani arrived in Damascus on Friday. He is expected to meet President Bashar al-Assad. Iran is Assad's strongest ally in the region.

Syria's conflict erupted in March 2011 with an uprising against Assad's regime, inspired by other Arab Spring revolts. The crisis has since morphed into a civil war. More than 40,000 people have been killed in the unrest, according to activists.

On Wednesday, Syrian warplanes flattened a building next to a hospital in Aleppo, killing at least 15 people and damaging one of the last remaining sources of medical help for civilians in the northern city, activists said Thursday.

Once a private clinic owned by a businessman loyal to President Bashar al-Assad, the Dar al-Shifa hospital became a field hospital run by volunteer doctors, nurses and aides united by their opposition to the regime and the need to give medical care to both civilians and rebels.

The facility has taken at least six direct hits in recent months, mostly affecting the upper stories.

On Wednesday night, warplanes bombed a building adjacent to the hospital, turning it into a pile of rubble and spraying shrapnel and debris into Dar al-Shifa itself, activists said.

Rami Abdul-Rahman, chief of the Syrian Observatory for Human Rights, said at least 11 fighters were killed in the airstrike, in addition to a doctor, a young girl and two children who were on the street.

Another activist group, the Local Coordination Committees, confirmed the bombing and identified the doctor as Mohammad Qassem Agha. The group said 40 people died in airstrikes in Aleppo on Wednesday, but did not say how many died in the hospital strike.

Videos posted online by activists showed the flattened building and substantial destruction in front of the hospital. Residents and armed rebels, and in one instance, a doctor wearing green scrubs are seen picking through the rubble and overturned gurneys at the entrance of the hospital.

In one video, a man is seen calling for survivors under the rubble while a man is heard crying for help underneath a huge slab of concrete.

The seven-story hospital stands only 400-500 yards from the front line in a neighborhood that is heavily shelled on daily basis.