Warplanes have bombarded a district housing Palestinian refugees in the Syrian capital for the first time since the anti-regime uprising began.
Reports on Sunday suggested that a mosque sheltering people who had fled violence in nearby suburbs was hit and at least eight people were killed.
Video posted online, purporting to show the aftermath, showed several bodies and destruction.
"Warplanes staged an airstrike on an area near al-Bassel hospital... in Yarmouk camp, hurting several people," the UK-based Syrian Observatory for Human Rights said.
The district has seen clashes between government troops and rebels and been bombarded earlier in the conflict but Sunday was the first time air power was used, according to activists.
Yarmouk is a residential area where Palestinians and Syrians from the Israeli-occupied Golan Heights have lived for decades. Since violence intensified in and around Damascus in summer, residents from nearby neighbourhoods which have seen intense fighting between rebels and government troops have taken shelter in the area.
Palestinian President Mahomud Abbas appealed on Sunday for an immediate halt to firing on Palestinian refugee camps in Syria.
"We call on the warring sides in Syria to spare the Palestinian people and their camps in Syria," Abbas said in a statement carried by official Palestinian news agency WAFA, adding that bombing of the refugee camps "must be stopped immediately."
"We also call on the international community to take immediate action to provide protection to our people in Syria," Abbas said, adding that the Palestinians were "not involved" in the conflict.
As the Syrians, Palestinians have been divided over the uprising, with some taking up arms against the regime and others fighting to defend it.
Yarmouk is part of an arc sweeping from the east to southwest of the Syrian capital where government troops have been trying for several weeks to push back rebels.
Activists also reported bombardment of the nearby districts of Hajar al-Aswad and Assali.
Meanwhile, Alaeddin al-Sabbagh, former head of public relations in the Syrian intelligence, announced his defection while speaking to Al Jazeera.
He said he had been in touch with rebels for some time and that they knew he was serving the revolution while he was in office.He called Assad's regime a "clinically dead" one.
The opposition says more than 40,000 people have been killed since the uprising started in March last year and gradually turned into a civil war. Hundreds of thousands have fled to neighbouring countries and many more have been displaced internally.