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.

Reuters cannot independently verify the video.

Rebels are trying to stem an attempt by President Bashar Al-Assad's forces to drive them out of this northern city.

Syria's 27-month conflict appears to be reaching a turning point, after a strategic gain earlier this month by Assad's forces.

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.

Other activist video purports to show a government tank shelling the Qaboun district in the north Damascus suburbs.

Rebel prospects for reversing Assad's gains in Damascus may now hinge on military support from Western and Arab backers.