BEIRUT -- Battles between security forces and rebels rocked Syria's capital for the third consecutive day Tuesday and appeared to be spreading to other districts of the city.
Opposition activists were calling the fighting -- the fiercest clashes to date reported in Damascus -- a potential turning point in the 16-month civil conflict, which previously had left the capital mostly unscathed.
A senior figure in the rebel Free Syrian Army, the main insurgent group, said Tuesday that the "battle for the liberation of Damascus has begun,” according to a Lebanese website tracking the conflict.
Col. Qassim Saadeddine, Homs-based spokesman for the Joint Command of the rebel group, said the fighting will not stop until the whole of the capital has been conquered, reported the website of a Lebanese television station.
"We have transferred the battle from Damascus province to the capital," Saadeddine is quoted as saying. "We have a clear plan to control the whole of Damascus. We only have light weapons, but it's enough."
However, it appeared that the government of President Bashar Assad maintained control of key state installations and thoroughfares. Military reinforcements were said to have been brought into the capital and rushed to battleground districts. Video from the capital showed armored vehicles rumbling down main roads.
It was difficult to ascertain if the clashes signaled an all-out insurrection in the capital or violent eruptions in certain restive neighborhoods. It seemed possible that the violence could escalate and signal a new phase in the conflict.
Shaken residents of the capital reported the sounds of gunfire and shelling. There were reports of machine gun fire in central Sabaa Bahrat Square and nearby Baghdad Street, in the center of the capital.
The opposition said government forces were using attack helicopters and shelling to quell the unrest. There were unconfirmed reports that rebels had shot down a helicopter gunship.
Video posted on the Internet purported to show tanks rumbling in the central district of Midan, near the old walled city.
The Syrian Observatory for Human Rights, a Britain-based opposition group, said military reinforcements were dispatched to Midan amid intense clashes between armed rebels and regime forces.
The official Syrian Arab News Agency said authorities “continue to chase down an armed terrorist group in the outskirts” of Midan, “inflicting heavy losses in the terrorists’ ranks.” The government typically refers to the rebels as terrorists.
Violence was also reported in the eastern district of Qaboun, where government forces attacked overnight with helicopters, said one opposition activist reached by telephone. An opposition group said helicopter fire had destroyed a number of buildings in the district.
The official news agency said rebels had attacked an electricity converter station in Qaboun with mortars and rocket-propelled grenades. The station will be out of service for two days, the official news service said.
Insurgents in Syria have repeatedly targeted electrical stations, fuel pipelines and other strategic facilities, the government says.
Unrest has also reportedly spread to several rebellious suburbs, including Barzeh in the north and Douma in the northeast. Both districts have long been anti-government bastions. The Syrian Observatory for Human Rights said the government was deploying helicopters in the orchards of Barzeh, apparently targeting insurgents.
An opposition activist reached by telephone in Damascus described a scene of battle.
"There is gunfire, sounds of explosions -- you can see helicopters above Qaboun and Barzeh," said the activist, who asked to be identified only as Susan for security reasons. "There are large columns of smoke and there are shelled areas. Wounded people ... some killed. We can't help them because there are snipers on rooftops. The situation is really difficult today ... shelling, sounds of gunfire. ... People are trying to run away, but the snipers shoot madly."
More government mortar fire was reported Tuesday in the southern district of Tadamoun, where the violence initially broke out on Sunday.
The official Syrian government news service also said that security forces clashed with insurgents attempting to block roads in the capital’s southern Naher Aisha district.
The Local Coordination Committees, an opposition coalition, said at least 11 people were reported killed in clashes in the capital. The figure could not be corroborated.
The Syrian government has severely restricted the entry of journalists and human rights monitors, making it difficult to judge the extent of the violence in Damascus and elsewhere in Syria.
-- Alexandra Sandels. Patrick J. McDonnell in Istanbul contributed to this report.
Photo: A picture released by the Syrian opposition's Shaam News Network on Tuesday purports to show opponents to the regime blocking a road with burning tires in the Jobar neighborhood of Damascus the day before. The information could not be independently verified. Credit: Shaam News Network / Agence France-Presse / Getty Images.