Syrian rebels seized a key military base with artillery stockpiles in the country's east Thursday, strengthening their hold in an oil-rich strategic province bordering Iraq, activists said.

The rebels have been making advances in the Deir el-Zour province recently, and the capture of the base followed the seizure of a military airport in the same area last week.

Activist groups and a local fighter told The Associated Press the Mayadeen base fell in the morning hours, after a three-week siege. The fighter spoke on condition of anonymity because of security concerns.

The base was considered the last stronghold for regime forces in the eastern province, according to the Syrian Observatory for Human Rights.

In Damascus, two mortar shells struck the upscale neighborhood of Mazzeh during the morning rush hour Thursday, injuring at least one person, Syrian state TV said.

The report blamed "terrorists" for the attack, a term the government uses for opposition fighters.

The neighborhood is home to a number of foreign embassies and has been targeted several times in the past few days. On Tuesday, two mortars struck the Information Ministry building, causing material damage.

An AP reporter at the scene of the Damascus blasts said one of the shells burned a six-floor apartment in a residential building, seriously injuring one woman. The second mortar struck and damaged the first floor in a building across the street.

Nizar Hamdi, a 38-year-old owner of a computer center, said the timing of the blast coincided with the time students head to school.

"This is a residential area and there are no military bases here. So why are they targeting civilians?" he said.

Syrian TV showed a girl wearing the school uniform who said the mortar fell as she was preparing herself to go to school.

"It was terrifying, I couldn't go to school. People were screaming," she said.

The Syrian capital _ the seat of President Bashar Assad's power _ has seen scores of attacks in the past months and a growing number of car bombs and mortar attacks by rebels determining to oust him.

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, with scores of rebel groups across the country fighting government troops. Nearly 40,000 people have been killed in the 20 months of unrest, according to activists.

In Aleppo, Syria's northern business and commercial hub, government troops and rebels have been locked in a deadly stalemate for months.

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

Once a private clinic owned by a businessman loyal to President Bashar Assad, the Dar al-Shifa 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 floors. The seven-story hospital is only 400-500 meters (yards) from the frontline in a neighborhood that is heavily shelled every day.

The warplanes turned the building adjacent to the hospital into a pile of rubble and sprayed shrapnel and debris into Dar al-Shifa itself, activists said.

Rami Abdul-Rahman, chief of the Britain-based Observatory, said at least 11 fighters were killed in the raid, 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 significant destruction in front of the hospital. Residents and rebels, along with a doctor in green scrubs are seen picking through the rubble and overturned gurneys outside the hospital entrance.

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

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Associated Press writer Albert Aji in Damascus, Syria, contributed to this report.