Moscow's top diplomat arrived in Syria Tuesday for talks with embattled President Bashar al-Assad, state television reported, as regime troops besieging Homs renewed heavy shelling of the protest city.

Thousands of regime supporters waving Syrian flags lined the streets as Foreign Minister Sergei Lavrov's motorcade travelled through Mazzeh neighbourhood on its way from the airport, television footage showed.

Many chanted, "Thank you Russia, thank you China."

"I want to thank Russia and China for their stand in support of the Syrian people," one woman said.

The Russian foreign ministry confirmed the arrival of Lavrov and Russian Foreign Intelligence Service head Mikhail Fradkov but gave no further details on the visit, the precise purpose of which has been kept tightly under wraps since it was first announced at the weekend.

Ahead of their arrival, reports had said that Lavrov and Fradkov could try to persuade Assad to quit.

However the defiant regime, which has been rocked by an uprising for almost 11 months, was in no mood to make any concessions.

Government troops on Tuesday renewed their deadly assault on Homs for a fourth day, targeting parts of the city under the control of army defectors with rockets and shells.

And in a statement carried by SANA state news agency, Syria's interior ministry vowed to push on with its onslaught on Homs in a bid to rid the region of what it said were "armed terrorist gangs."

"Operations to hunt down terrorist groups will continue until security and order are re-established in all neighbourhoods of Homs and its environs and until we overcome all armed persons terrorising citizens and threatening their life," it added.

Shooting thought to be from outgunned rebels echoed across the Homs neighbourhood of Baba Amr in the morning in response to the new wave of shells and rockets.

Abu Rami, an activist AFP reached by telephone from Beirut, said the explosions had continued through the night.

"There are about four blasts every five minutes," he said. "Since this morning the shelling has been concentrated in the neighbourhoods of Baba Amr, Inshaat and Jubar.

"The humanitarian situation is dire. No one can move around. There are snipers everywhere," he added.

Other activists reached by telephone have said food and medicine were in short supply.

The clashes come a day after nearly 100 civilians were killed across Syria, activists said, with the majority dying in the fierce onslaught on Homs and its environs, according to the Syrian Observatory for Human Rights.

Rights groups say more than 6,000 people have been killed since the outbreak of the revolt mid-March.

A resident of Homs told AFP that Monday's assault was unprecedented. It had began at around dawn, with barrages of rockets, mortar rounds and artillery shells.

"What is happening is horrible, it's beyond belief," said activist Omar Shaker, reached by telephone as loud detonations were heard in the background. "There is nowhere to take shelter, nowhere to hide."

Lavrov's trip comes days after Russia disgusted the West and Syrian opposition activists Saturday by vetoing along with China a UN Security Council resolution condemning the Assad regime's crackdown on protesters.

Speaking to reporters on Monday, Lavrov refused to divulge the purpose of the mission.

"When you go on a mission on the order of the head of state then the purpose of the mission is usually only revealed to the person it is addressed to. If I tell you everything now, then what is the point?" he said.

Russia has so far offered no clues on the role to be played by Fradkov, who heads an ultra-secret organisation that is the successor to the KGB.

Western powers were outraged at the vetoes of Russia and China, with US Secretary of State Hillary Clinton calling them a "travesty."

US President Barack Obama shied away from talk of military intervention and vowed to pursue diplomatic means.

"It is important to resolve this without recourse to outside military intervention and I think that's possible," he said in an NBC television interview.

Russia and China both defended their vetoes, with Lavrov on Monday saying that the reactions from Western capitals were "indecent and bordering on hysteria."

Beijing expressed hope that Lavrov's visit to Damascus would succeed, and said it was considering sending its own envoys to the Middle East to help resolve the conflict.

Meanwhile, the Syrian opposition urged businessmen across the strife-torn country and throughout the Arab world to fund rebel forces seeking the overthrow of Assad's regime.

"We are sending a warm appeal to Arab and Syrian businessmen to take part in an efficient and direct way in the legitimate financing of self-defence operations and the protection of civilian areas carried out by the Free Syrian Army," a joint statement issued by the Syrian National Council and the FSA said

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