Baba Amr neighbourhood in Homs targeted by shelling

Another clip shows a car on fire, which the cameraman says was "destroyed by Assad's brigades in Baba Amr neighbourhood".

"Arabs and Muslims where are you? We are being destroyed and being bombarded," he adds.

Other footage, also purportedly shot on Tuesday, showed tanks in Homs and a military checkpoint in Aleppo. Military vehicles believed to be carrying weapons in Daraa was also released on Monday.

A flood of military reinforcements has been a prelude to previous offensives by President Bashar Assad's authoritarian regime, which has tried to use its overwhelming firepower to crush an opposition that has been bolstered by defecting soldiers and hardened by 11 months of street battles.

On Tuesday, Russia said the United Nations should send a special envoy to Syria to help coordinate security issues and the delivery of humanitarian assistance.