Syrian activists called for a "day of defiance" in Damascus Sunday after security forces shot dead a mourner at a funeral that turned into one of the largest anti-regime rallies ever seen in the capital.

"We expect huge demonstrations," in Damascus, Deeb al-Dimashqi, a member of the Syrian Revolution Council based in the capital told AFP, adding that Syrian forces had clamped tight security around the city.

"There is a large security presence," he said, adding that demonstrators were expected to defy the clampdown and stage demonstrations in several parts of the city, including in Mazzeh, where the mourner was killed on Saturday.

In a message to Damascus residents on their "Syrian Revolution 2011" Facebook page, activists said: "The blood of the martyrs exhorts you to disobedience."

Saturday's funerals were for four people, two of them teenagers, killed when security forces fired on protesters Friday in the same district, which is overlooked by the presidential palace and houses many government offices and embassies, according to human rights group and activists.

"The funerals in Mazzeh turned into protests -- it was the closest major gathering to Omayyad Square" in the city centre, the head of the Syrian Observatory for Human Rights, Rami Abdul Rahman, told AFP.

Mohammed Shami, a spokesman for activists in Damascus province, echoed him.

"It's the first time there have been demonstrations of such a scale so close to the centre of Damascus," Shami said of Saturday's funeral, adding that some 15,000 people had turned out despite snowfall.

He said the shootings during the funerals, in which many people were wounded, were followed by a "wave of searches and arrests" across the leafy, upscale residential district.

"People hid wherever they could," he said. "State television didn't cover what happened even though it was only a short distance from the Radio and Television Organisation."

Activists described demonstrations held on Friday in Damascus as "unprecedented", saying there were 49 in all.

"We said from the onset that the day when huge demonstrations will spill out in Damascus and (Syria's second city) Aleppo, it will be the end of the regime," said Agnes Levallois, a Paris-based Middle East expert.