Syrian forces tightened their grip on the outskirts of Damascus on Monday, as Europeans prepared to send top diplomats to lobby for a UN resolution condemning President Bashar al-Assad's regime.

The Syrian opposition flatly rebuffed a Moscow call for talks with the Assad regime as violence across Syria killed 29 people, mostly civilians, activists said.

On Sunday, 80 people were reportedly killed, equally divided between military and civilian deaths, in the most intense clashes since the 10-month-old uprising began, the Syrian Observatory for Human Rights said.

Regime forces, who were reported to have executed a founder of the rebel army, appeared determined to wrest back control of Damascus suburbs which have intermittently fallen into the hands of the rebels.

Near the capital, troops penetrated Rankus, 40 kilometres (25 miles) north of the capital, after having shelled the town which the army had encircled for the past six days, the Observatory said.

Activists at the scene said deserters pulled out of Rankus as the army moved in, while, in the eastern suburbs, snipers were "shooting at everything that moves" in Irbin and Hammuriyeh.

Across the area, government soldiers have set up checkpoints at strategic crossroads in search of rebel fighters or suspects wanted by security services.

The Observatory said at least 17 civilians were killed in central Syria when security forces stormed the flashpoint city of Homs, killing a family of six and a young girl.

Free Syrian Army Colonel Hussein Harmush, a founder of the rebel group formed from army defectors, was executed last week, said the Syrian League for Human Rights, in a report which could not be independently confirmed.

In June last year, Harmush became the first Syrian officer to publicly declare his opposition to the regime's deadly crackdown on protesters.

Harmush left Syria to seek asylum in Turkey, where he established the Brigade of Free Officers, a group of dozens of deserters later absorbed into the Free Syrian Army headed by Riyadh al-Asaad.

Months later, his "confessions" were aired on Syrian state television after his return home in unclear circumstances.

Elsewhere, rebel soldiers on Monday "attacked a minibus carrying six security officers on their way to make arrests in Hirak, killing all of the passengers," the Observatory said.

Government forces responded by deploying two tanks which opened fire and killed three civilians in the town in Daraa province, south of Damascus, it said.

The latest spike in violence, on top of what the United Nations said at the start of January already added up to 5,400 killings, pushed the Arab League to suspend its mission to Syria on Saturday.

League chief Nabil al-Arabi, who is expected in New York on Monday to try to lobby for a UN resolution condemning Syria, said the decision was taken after Damascus "chose the option of escalation".

French Foreign Minister Alain Juppe is to head to New York on Tuesday to press the Security Council into taking action over the Assad regime's "crimes against humanity", his ministry said.

Foreign ministry spokesman Bernard Valero said a ministerial meeting at the UN on Tuesday would allow the Security Council to listen to the Arab League's report on the situation in Syria.

The Foreign Office in London said that Foreign Secretary William Hague would also go to the Security Council although Juppe admitted that "conditions aren't yet right to get a resolution passed, because Russia is still reluctant."

Arabi said on Sunday he hoped Moscow and Beijing would alter their position and allow the Security Council to adopt a resolution backing a new League plan to end the crisis.

The plan calls for Assad to hand his powers to his deputy to clear the way for a transitional government of national unity and elections -- a formula flatly rejected by Damascus.

Moscow, which has close ties with its Soviet-era ally and opposes the UN draft resolution, said on Monday that Syrian authorities had agreed to its offer to host talks with opposition representatives.

But the head of the Syrian National Council said that the opposition rejects all talks with the Damascus regime until Assad steps down.

"The resignation of Assad is the condition for any negotiation on the transition to a democratic government in Syria," Burhan Ghalioun told AFP.