Navi Pillay, the UN rights chief, has issued an appeal for urgent international action to protect civilians in Syria, as government forces continued a relentless assault on the city of Homs.

"I am appalled by the Syrian government's wilful assault on Homs, and its use of artillery and other heavy weaponry in what appear to be indiscriminate attacks on civilian areas in the city," a statement from the Office of the UN High Commissioner for Human Rights said.

Activists said that the army was firing rockets and mortar rounds to subdue opposition districts and tanks entered the Inshaat neighbourhood and moved closer to Bab Amr.

More than 50 people have reportedly been killed in the city on Wednesday.

Al Jazeera's Rula Amin reports from Beirut in neighbouring Lebanon.