DAMASCUS  - Syrian troops and pro-regime militias stormed and torched a southern town on Saturday, reports said, as UN observers visited a central village where a mass killing has provoked harsh global condemnation.

Hundreds of soldiers backed by helicopter gunships attacked Khirbet Ghazaleh in the province of Daraa - the cradle of a 16-month uprising - amid heavy gunfire, the Syrian Observatory for Human Rights said.

An activist on the ground who identified himself as Bayan Ahmad gave a similar account, saying pro-regime militias were setting alight houses in the town.

"The army entered without resistance as the rebel Free Syrian Army left town. The shelling has wounded dozens of people but we don't have medical resources to treat them," he added. Elsewhere, a pregnant woman was among 28 people killed across the country, the Observatory said, a day after 118 people died including dozens of civilians gunned down by troops at anti-regime protests.

An AFP journalist said fighting Saturday near the Turkish border between government troops and rebel fighters left at least 10 rebels dead and 15 wounded.

The violence persisted despite international outcry over the killing on Thursday of more than 150 people in the central village of Treimsa.

The circumstances surrounding the incident have still not been clarified, but UN observers made their way to the village in the central province of Hama on Saturday to investigate. Spokeswoman Sausan Ghosheh told AFP that a group of observers had entered Treimsa, while an activist calling himself Abu Ghazi said they had met residents and "inspected places that were bombed and where there were traces of blood."

On Friday, a reconnaissance mission had gone in to the village to assess the situation, Ghosheh said.

Rebel leader Abu Mohamad, whose fighters are based near Treimsa, had said more than 200 people were slaughtered there.

The Observatory was more cautious, saying "several dozen rebel fighters were among those killed," adding that only around 40 of the dead had been identified, while 30 were burned and 18 were "summarily executed".

A spokesman for Syria's military said the army killed "many terrorists" in Treimsa, but no civilians, in a "special operation... targeting armed terrorist groups and their leadership hide-outs."

Observatory head Rami Abdel Rahman told AFP it "might be the biggest massacre committed in Syria since the start of the revolution."

If confirmed, the 150-person toll would exceed that of a massacre at Houla on May 25, when a pro-Assad militia and government forces were accused of killing at least 108 people.

Treimsa, which had a population of 7,000, "is empty now. Everyone is dead or has run away," an activist calling himself Abu Ghazi said.

Treimsa is near Al-Kubeir, where at least 55 people were killed on July 6, according to the Observatory. Like Al-Kubeir, Treimsa is a majority Sunni village situated near Alawite hamlets.

The US ambassador to the United Nations, Susan Rice, said on Twitter that the killings "dramatically illustrate the need for binding measures on Syria" by the council.

Western nations have proposed a resolution that would impose sanctions on the regime of Syrian President Bashar al-Assad over the conflict, which rights activists say has cost more than 17,000 lives.

Britain, France, the United States, Germany and Portugal have proposed a resolution that would give Assad 10 days to stop the use of heavy weapons, in line with the Annan plan, or face sanctions.

They only want to give the UN observer mission a new 45-day mandate.

But Russia has rejected any use of sanctions and is proposing a rival resolution that renews the mandate of UNSMIS, which ends on July 20, for 90 days and has said sanctions are unacceptable.

French President Francois Hollande called on Russia and China not to oppose sanctions and during a televised interview with channels TF1 and France 2 said, "I told (Russian President Vladimir) Putin... that the worst thing is to have a civil war in Syria."

"So we have to find a political position that avoids civil war. There is still time, it is high time," Hollande said.

Turkish Prime Minister Recep Tayyip Erdogan on Saturday branded the killings in Treimsa as "attempted genocide" and said the regime was doomed.