Syrian troops and rebels clashed inside the tightly controlled capital on Monday for the second day in what activists called some of the worst fighting since the country's crisis began 16 months ago.
The fighting, which was concentrated in the districts of Kfar Souseh, Midan and Tadamon, briefly closed the highway linking the capital with Damascus International Airport to the city's south, said Mustafa Osso, an activist.
"The capital used to be safe. This will trouble the regime. It seems there is a new strategy to bring the fighting into the center of the capital," Osso said.
An amateur video posted online showed Kfar Souseh as the sound of intense gunfire could be heard at a distance and the presidential palace seen in the background.
There have been sporadic clashes in Damascus in recent months, although President Bashar Assad's forces remain firmly in control of the capital. Many of the Damascus suburbs, however, have risen up against the regime, prompting a ferocious response from the military.
A Damascus resident who spoke on condition of anonymity said gunfire and sporadic explosions could be heard throughout the morning unlike previous clashes which occurred at night, which was a sign that the rebels were becoming more brazen.
The clashes come as Russian foreign minister Sergey Lavrov on Monday accused the West of using blackmail to secure a new UN Security Council resolution that would authorize the use of force in Syria.
On Sunday, the crisis crossed an important symbolic threshold as the International Red Cross declared the conflict a civil war with potential for increasing war crimes prosecutions.
The UN observers also gathered new details on the killings in the village of Tremseh.