Elite forces loyal to Syrian President Bashar al-Assad pounded a rebel bastion in Homs on Thursday in what appeared to be a final push on the opposition stronghold, activists said.

A senior official in the rebel Free Syrian Army told Reuters rebels in the district of Baba Amro were fending off more than 7,000 government troops. Opposition forces had promised to step up attacks elsewhere in Syria to try to relieve the pressure.

"Baba Amro will be the straw that will break the regime's back," Mohaimen al-Rumaid told Reuters from an area in Turkey near the Syrian border.

"All of Syria is turning into Baba Amro."

Heavy shelling resumed overnight after several hours of sporadic bombardment, opposition sources in the city said.

They said rebels had repelled an attempt by government forces to advance into Baba Amro from the Hakoura area on its northern edge, but diplomats said earlier Syria's feared 4th Armoured Division seemed determined to overrun the district.

"All the signs out of Homs are that they're trying to finish it off," a senior Western diplomat said.

A motley band of army deserters and desperate insurgents who call themselves the Farouq Brigade of the Free Syrian Army have sworn to fight to the last man, one activist from Baba Amro told Reuters. Others, though, said some of the unit's leaders had already made their escape from the shattered neighbourhood.

Rumaid admitted the rebels were far outgunned, armed with machineguns and mortars against armoured forces backed by heavy artillery and rockets but said they were holding out.

"Infantry fighting goes on. The men are still resisting and Assad's army is shelling Baba Amro but it has not gone deep beyond its parameters," said Rumaid, a member of the Higher Military Council overseeing the Free Syrian Army.

Activists say hundreds of civilians have been killed in besieged opposition districts of Homs. Shells and rockets have been crashing into Baba Amro since Feb. 4. Army snipers pick off civilians who venture out.

Reports from the city could not immediately be verified due to tight government restrictions on media work in Syria, where Assad is facing the gravest challenge of his 11-year rule.

Western and Arab governments, which have already called on Assad to step down and end the bloodshed, expressed mounting concern for the fate of civilians trapped in Homs.

"I am appalled by reports that the Assad regime is preparing a full-scale land assault on the people of Homs," Britain's Foreign Secretary William Hague said, calling for immediate access for aid.

The 4th Armoured Division commanded by Maher al-Assad, the president's younger brother, has won a reputation for ruthlessness during the past year of revolt against the government.

Drawn from the Alawite sect to which the Assads belong, it is hated by many in the Sunni majority who recall the role its predecessor units played in massacring many thousands of Sunni Islamists at Hama in 1982 on the orders of Assad's father Hafez.

The United Nations says Assad's security forces have killed more than 7,500 civilians since the revolt began last March. Syria's government said in December that "armed terrorists" had killed more than 2,000 soldiers and police during the unrest.

The opposition Syrian National Council made a new appeal for international help on Wednesday evening, urging the UN-Arab League envoy on Syria, Kofi Annan, to go to Baba Amro "tonight".

Annan said in New York he expected to visit Syria "fairly soon" and urged Assad to engage with efforts to end the turmoil.

A spokesman for the International Committee of the Red Cross, Hicham Hassan, said the violence in Homs was making the humanitarian situation more difficult.

"This makes it even more important for us to repeat our call for a halt in the fighting," he told Reuters in Geneva.

The ICRC said its Syrian Red Crescent affiliate had established 10 distribution and first aid points in Homs, but had been unable to operate in Baba Amro because of the violence.

UN humanitarian chief Amos said she was "deeply disappointed" Syria refused to let her visit the country, where she had hoped to assess the emergency relief needs in besieged towns.  - Reuters