BEIRUT, June 25 (Reuters) - Syrian forces loyal to President Bashar al-Assad hit rebel-held eastern districts of Damascus on Tuesday with mortar bombs, artillery and air strikes, opposition activists said.
The assault was focused on Zamalka and Irbin, on the edge of the government-controlled centre of the capital, according to the pro-opposition Syrian Observatory for Human Rights.
Rebels in the capital's outskirts say they are facing a slow but steady army advance. A rebel push into the city a year ago was seen at the time as heralding Assad's fall, but his forces, with support from his Shi'ite Muslim allies, have fought back.
If they retake eastern districts of Damascus, mostly Sunni Muslim rebels would lose arms supply routes and suffer a severe blow in their drive to end four decades of Assad family rule.
"The areas of Irbin and Zamalka were exposed to bombings by regular forces, mortar bombs and heavy artillery," the British-based Syrian Observatory said. It said there were reports of casualties from air raids, but gave no details.
Rebels say their prospects for reversing Assad's gains in Damascus may now hinge on military support from Western and Arab backers. The United States announced unspecified military aid this month.
More than 93,000 people have been killed in the Syrian conflict, which began as a popular anti-Assad protest movement but has descended into a civil war with sectarian overtones.
Nearly 1.7 million refugees have fled into neighbouring countries, including Lebanon, where clashes between armed groups supporting opposing sides in Syria have fuelled fears of a lapse back into sectarian civil war.
Lebanon is still struggling to heal the wounds of its 1975-90 civil war.
The Beirut government is trying to restore calm after Sunni militiamen clashed with the army this week in the coastal cities of Sidon and Tripoli. They accuse the army of backing Lebanon's Shi'ite Hezbollah group fighting on Assad's side.
(Reporting by Oliver Holmes)