Syrian forces bombarded opposition-held neighbourhoods of the city of Homs with rocket and mortar fire yesterday as divided world powers struggled to find a way to end the violence.

The UN has condemned the government's assault on Homs in the heart of a revolt that broke out nearly a year ago.

"I fear that the appalling brutality we are witnessing in Homs, with heavy weapons firing into civilian neighbourhoods, is a grim harbinger of things to come," UN secretary-general Ban Ki-moon said after briefing the security council in New York.

Hundreds of people have been killed over the past week as President Bashar al-Assad forces try to stamp out opposition in Homs.

As yesterday dawned, rocket and mortar fire rained down again on Baba Amro, Khalidiya and other districts. Armoured government reinforcements also poured into the eastern city.

A Syrian doctor, struggling to treat the wounded at a field clinic, launched an emotional video appeal on the internet for the killings to stop.

As concern grew over the plight of civilians, the US said it was considering ways to get food and medicine to them, a move that would deepen international involvement in a conflict that has wide geopolitical dimensions and has caused division among foreign powers.

Before flying to Washington for talks on Syria, Turkish Foreign Minister Ahmet Davutoglu said that Turkey, which once saw Assad as an ally, could no longer stand by and watch. Turkey wanted to host an international meeting to agree on ways to end the killings and provide aid, he said.

"It's not enough being an observer," he said, though Russia and China have warned against "interference".

Foreign ministers of the Arab League, which Ban said was planning to revive an observer mission it suspended last month, are due to meet in Cairo on Sunday.

They may want to hear other governments' ideas by then.