Description:Syria's five-day-old ceasefire appears to be crumbling on Tuesday, with the Syrian government launching a barrage of shells and mortars into the already-battered opposition stronghold of Homs. This video, posted to a social media website by activists - and which cannot be independently verified by Reuters - shows smoke rising from buildings, purportedly in the districts of Bayadiya and Khalidiya. The violence comes after the arrival in Damascus of an advance team of United Nations monitors.(1:01)