Fighting between soldiers and rebels broke out on Wednesday for the first time near two Christian districts of Damascus, the Syrian Observatory for Human Rights said.
"Fighting erupted at dawn on Wednesday on the outskirts of the Bab Tuma and Bab Sharqi neighbourhoods. First indications are that one soldier has been killed," the Britain-based group said in a statement.
"This is fighting in areas where it has not happened before. These are areas where the rebels have so far not had access," Observatory chief Rami Abdel rahman told AFP.
One witness said rebels attacked a military position outside Bab Sharqi at 4:00 am (0100 GMT) in a clash that lasted for 15 minutes.
An AFP correspondent said calm later returned to the area.
Bab Tuma and Bab Sharqi are traditional Christian quarters in the Old City of Damascus, previously popular with tourists and the location of several hotels. They have also been the scene of several pro-regime protests in the past.
Earlier the Local Coordination Committees (LCC) that organises protests on the ground, reported a blast and heavy gunfire from Baghdad Street, a main arterial route through the city.
The LCC also said that the capital's southern suburb of Tadamun was hit by mortar fire at dawn.
Damascus residents heard explosions and intermittent gunfire late on Tuesday in several districts, notably in the southwestern neighbourhood of Kfar Sousa.
Fighting in that district broke out again on Monday after a lull when rebels attacked a checkpoint of regime forces using rocket-propelled grenades.
Since July 20, the battle between the rebels and government forces has focused on the country's commercial capital Aleppo in the north.
On Tuesday 154 people -- among them 35 civilians, 63 soldiers and 27 rebels -- were killed in violence nationwide, around half in Aleppo.
Both troops and rebels poured into Aleppo on Tuesday as both sides battened down for the long haul after 40 police were killed on day four of a pivotal battle in the nearly 17-month conflict.
According to the Britain-based Syrian Observatory for Human Rights, more than 20,000 people have been killed since the uprising broke out in mid-March last year.
There is no way to independently verify the figure, while the UN has stopped keeping count.© ANP/AFP