Amateur video uploaded to a social media website purports to show Syrian rebel forces engaged in fierce fighting in Syria's second city, Aleppo, Thursday.<br/> <br />Reuters cannot independently verify the video.<br/> <br />Rebels are trying to stem an attempt by President Bashar Al-Assad's forces to drive them out of this northern city.<br/> <br />Syria's 27-month conflict appears to be reaching a turning point, after a strategic gain earlier this month by Assad's forces.<br/> <br />This video segment, said to be filmed in Aleppo Thursday, and also unverified by Reuters, purports to show rebels engaged in gunfights, as they come under shelling from government artillery.<br/> <br />Other activist video purports to show a government tank shelling the Qaboun district in the north Damascus suburbs.<br/> <br />Rebel prospects for reversing Assad's gains in Damascus may now hinge on military support from Western and Arab backers.