Mortar fire reported in central Damascus

This image taken from a Syria opposition member's online video appears to show cluster munition remnants found in the area surrounding Hama, Syria, according to Human Rights Watch.
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Hama cluster bomb munitions
This image taken from a Syria opposition member's online video appears to show cluster munition remnants found in the area surrounding Hama, Syria, according to Human Rights Watch.
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(CBS News) Clashes between Syria's increasingly aggressive armed rebels and government forces erupted into mortar fire Thursday right in the heart of the capital city - President Bashar Assad's stronghold, according to opposition activists.

There were conflicting reports as to which side had fired the mortars around the upscale Kafar Souseh neighborhood in central Damascus. Some rebels claimed online it was their own forces firing at the government's Mezze airbase, and others said it was regime forces lobbing artillery at the rural areas surrounding the neighborhood in an attempt to drive rebels away from Damascus.

The reports could not be independently verified, but Assad's fight against the rebels has been creeping slowly closer to his seat of power for weeks, and fighting in Kafar Souseh - an upscale area home to many embassies - would be unwelcome news for the dictator.

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U.S. Secretary of State Hillary Clinton referred to Assad's government on Thursday as a "crumbling regime" that was "struggling to hold onto large parts of the country."

Rebel forces already control most of the northern Idlib province, and signs that the violence is moving closer to Assad's front door have been increasing.

Areas on the outskirts of Damascus, notably the northern suburb of Douma, have been pummeled by artillery for weeks.

Human Rights Watch issued a report on Thursday, meanwhile, saying videos posted by opposition activists prove Assad's forces have used Russian-made cluster bombs in the fight against the rebels and their supporters.

The videos show small bomblets, and casings for the larger ordnance that delivers them, allegedly shot in the hard-hit area of Hama.

"These videos show identifiable cluster bombs and submunitions," said Steve Goose, Arms Division director at Human Rights Watch. "If confirmed, this would be the first documented use of these highly dangerous weapons by the Syrian armed forces during the conflict."

Opposition groups say more than 15,000 people have been killed by the regime since the uprising began about 17 months ago. It started as a peaceful protest movement, but Assad's rapid and brutal crackdown on dissidents sparked the rise of an armed rebel movement which has since benefited from material and moral support from outside nations in the region.

  • Tucker Reals

    Tucker Reals is the CBSNews.com foreign editor, based at the CBS News London bureau.