DAMASCUS - UN observers said Friday they witnessed blood on the walls and "a strong stench of burnt flesh" in the Syria massacre village of Al-Kubeir, heightening Western calls for tough sanctions against Damascus.

The reports of the grim scenes in the Hama province town were relayed from the United Nations in New York as Syrian activists reported more killings overnight.

Twelve people, eight of them women, were killed by Syrian army fire in the southern flashpoint town of Deraa, the Syrian Observatory for Human Rights said.

Diplomats in New York said Britain, France and the United States would quickly draw up a Security Council resolution proposing sanctions against Syria. "We will move fast to press for a resolution," one UN diplomat said.

More than 20 unarmed UN observers were allowed into Al-Kubeir on Friday, a day after they were shot at and prevented from entering the village.

"Inside some of the houses, blood was visible across the walls and floors. Fire was still burning outside houses and there was a strong stench of burnt flesh," UN spokesman Martin Nesirky said in New York, delivering a grisly account of the visit.

At least 55 people were killed on Wednesday in an assault on Al-Kubeir, according to the Syrian Observatory.

UN officials, unable to confirm that toll, have made it clear they believe government forces and allies were behind the attack on the mainly Sunni Muslim village surrounded by an Allawite population loyal to President Bashar al-Assad.

"Armoured vehicle tracks were visible in the vicinity. Some homes were damaged by rockets from armoured vehicles, grenades and a range of calibre weapons," Nesirky said.

Paul Danahar, a BBC correspondent travelling with the UN convoy, reported seeing gutted buildings in Al-Kubeir and no sign of life or bodies.

"In front of me there is a piece of brain, in the corner there is a mass on congealed blood," he wrote on Twitter.

He quoted activists as saying government forces had removed victims' bodies on Thursday while the UN observers were being hindered from reaching the village.

According to preliminary evidence, troops had surrounded Al-Kubeir and militia entered the village and killed civilians with "barbarity", UN chief Ban Ki-moon told the UN Security Council.

Damascus denied responsibility and, as it has done repeatedly in the past, blamed foreign-backed "terrorists", using its term for rebels fighters.

Violence in Syria during Friday left at least another 26 people dead, mostly civilians, the Syrian Observatory said.

Activists called for protests after weekly Friday prayers under the rallying cry of "Revolutionaries and traders, hand in hand until victory", reaching out to the middle classes in Syria's two main cities of Damascus and Aleppo.

Thousands of people took to the streets in several provinces, activists said, including in the capital where protesters braved a heavy security deployment.

More than 13,500 people have been killed in the crackdown on dissent that followed the eruption in mid-March 2011 of anti-government protests and the increasingly violent insurgency against Assad's regime, the Observatory says.

International envoy Kofi Annan called for "additional pressure" in the wake of the latest killings.

UN-Arab League envoy Annan said in Washington that he would discuss with US Secretary of State Hillary Clinton "how we can put additional pressure on the government and the parties to get the (UN-Arab League peace) plan implemented".

Annan said "everyone is looking for a solution" but acknowledged doubts about a peace deal he brokered, which calls for a ceasefire and dialogue to end more than a year of violence aimed at toppling Assad.

A UN diplomat, speaking anonymously, said "there will be action in the coming days to get a vote on a resolution which includes measures under Chapter VII of the UN Charter -- which would mean sanctions."

Chapter VII allows for sanctions and, in extreme cases, military action. Russia and China, infuriated by the NATO campaign in Libya last year, have vowed to oppose any military intervention.

Meanwhile leaders from the Syrian military opposition called on the international community to provide better arms and support as they battle to topple the Assad regime.

"Those who claim to support the Syrian opposition should begin by supporting people on the inside of Syria," said Hussein Sayyed, president of the Supreme Revolutionary Council, speaking by phone to a meeting in Washington.

In Moscow, Clinton's pointman on Syria, Fred Hof, met Russian diplomats in a bid to persuade Russia to back Assad's removal.

But Deputy Foreign Minister Mikhail Bogdanov said after the meeting that Russia had no information about a leadership change being planned in Damascus and pointedly failed to make any public call for one.

In other developments, the Red Cross said the situation was "extremely tense" in many parts of Syria and that it was attempting to deliver humanitarian aid to 1.5 million people.

Al-Kubeir was the second major massacre in Syria in two weeks. At least 108 people -- including 49 children -- were killed when forces attacked the town of Houla on May 25. The government has denied any role in both slaughters.