Regime forces launched a new blitz on the Syrian city of Homs yesterday, killing more than 50 people, activists said, as the UN weighed a joint mission with the Arab League to end the violence.

Shelling erupted at daybreak, killing 53 civilians in the besieged central city and burning several bodies beyond recognition, the Syrian Observatory for Human Rights said.

Government troops trying to crush opponents of President Bashar al-Assad have killed at least 400 people in a relentless six-day onslaught on Homs, activists say.

“The shells are raining down on us and regime forces are using heavy artillery,” said Ali Hazuri, a doctor in the Baba Amr district reached by telephone from Beirut.

Omar Shaker, an activist in Baba Amr also reached by phone, added that residents of the district were hiding on ground floors as there were no underground shelters.

“When you venture outside, you can see craters every 10 metres,” he said.

At least 83 people were killed across Syria yesterday, said the Britain-based Observatory.

Eleven died when a shell slammed into their house in the Homs neighbourhood of Inshaat, while six others were killed in Rastan, a restive town in the same province.

Elsewhere, rebels killed seven security forces members when they ambushed two buses at a bridge near the southern town of Daraa, cradle of the revolt, said the Observatory.

But in apparent reference to the same incident, SANA state news agency reported the authorities had made arrests as they foiled an attempt to steal a truck transporting cars in Daraa.

UN chief Ban Ki-moon said on Wednesday the “appalling brutality” of the assault on Homs “is a grim harbinger of worse to come.”

He launched the idea of sending a joint observer mission with the Arab League but the idea had a lukewarm reception from Western powers.

The head of the pan-Arab bloc, which suspended its month-long monitoring mission to Syria on January 28, spoke to the UN chief about the proposed mission, which would include a UN envoy.