Mortars rained down on a crowded marketplace in a Palestinian refugee camp in the Syrian capital, killing 21 people as regime forces and opposition fighters clashed on the southern outskirts of Damascus, AP quoted activists as saying Friday. The Britain-based Syria Observatory for Human Rights, which reported the deaths, said the shells hit Yarmouk camp Thursday as shoppers were buying food for the evening meal. An online video of the immediate aftermath of the Yarmouk attack showed bleeding and burnt bodies with people rushing about amid the smoke and the sounds of screaming. Government troops, however, have in the past attacked the camp, home to nearly 150,000 Palestinians. Palestinian refugees in Syria have tried to stay out of the 17-month old uprising but with Yarmouk nestled among neighborhoods sympathetic to the opposition fighters, its residents were eventually drawn into the fighting. Yarmouk's younger inhabitants have also been moved by the Arab Spring's calls for greater freedoms and have joined protests against President Bashar Assad's regime- and have died during demonstrations when Syrian troops fired on them. Just before the Thursday evening mortar attack, camp residents had demonstrated against the government, chanting slogans against Assad and praising the opposition Free Syrian Army, according to online videos.