**PLEASE NOTE: EDIT CONTAINS GRAPHIC MATERIAL**br br REUTERS CANNOT INDEPENDENTLY VERIFY THE CONTENTS OF THESE VIDEOS, WHICH HAVE BEEN OBTAINED FROM A SOCIAL MEDIA WEBSITEbr br Chaos in Damascus as shelling hits what is said to be a Palestinian refugee camp.br br Footage, which cannot be independently verified by Reuters, is said to show the aftermath of a mortar attack by Syrian security forces.br br Medical sources said at least 20 people were killed as they prepared to break the Ramadan fast.br br A separate video appeared to show victims inside the camp clinic.br br Opposition activists say government troops were battling rebel forces in a nearby district when the mortar rounds hit.br br More footage showed people gathering in protest at the camp which houses more than 100,000 people.br br Many chanted anti-regime slogans and praised Syrian rebels who have been fighting to bring down the government for 17 months.br br Sarah Charlton, Reuters.