Syrian troops and militiamen loyal to President Bashar al-Assad stood accused by opponents on Thursday of a new massacre of scores of villagers hours before a divided U.N. Security Council convenes to review the crisis.

If confirmed, the killings of at least 78 people at Mazraat al-Qabeer, near Hama, will pile on pressure for world powers to act, but there is little sign they can overcome a paralysis born of sharp divisions between Western and Arab states on the one hand and Assad's defenders in Russia, China and Iran.

Several activists who monitor the 15-month-old revolt gave accounts to Reuters that women and children were among the dead when the village in central Syria came under artillery bombardment before fighters moved in on the ground and shot and stabbed dozens of people to death.

Echoing descriptions of a massacre of 108 civilians at Houla on May 25, which U.N. observers attributed to Assad's troops and loyalist 'shabbiha' militia, the Syrian Observatory for Human Rights said, "Shabbiha headed into the area after the shelling and killed dozens of citizens, among them women and children."

Some activists said at least 40 of the dead were women and children. At Houla, near Homs, nearly half had been children.

In that earlier case, Assad himself condemned the atrocity but denied any hand in it and blamed opponents whom he described as foreign-backed 'terrorists'.

Shabbiha, drawn mostly from Assad's minority Alawite sect that identifies with the Shi'ites of Iran, have been blamed for the killings of civilians from the Sunni Muslim majority.

That has raised fears of an Iraq-style sectarian bloodbath and reinforced a wider regional confrontation between Iran and the mainly Sunni-led Arab states of the Middle East.

The main Syrian National Council opposition group responded to reports of the new massacre by calling for stepped-up military assaults on Assad's forces.

CEASEFIRE MONITORS

The failure of a ceasefire brokered by U.N. envoy Kofi Annan in March to halt the bloodshed has raised questions over its continued worth. Annan, the former U.N. secretary-general, is to brief the Security Council later on Thursday in New York.

A 300-strong force of U.N. truce observers has been in Syria for weeks and can be expected to investigate the accounts from Mazraat al-Qabeer, which came in under nightfall in Syria.

There was no immediate comment from the government, and events on the ground are difficult to verify as Syria tightly restricts access to international media.

Activists, including the Observatory based in Britain, called for an immediate investigation: "The Syrian Observatory for Human rights calls on the international monitors to go immediately to the area. They should not wait to tomorrow to investigate this new massacre," it said in a statement.

"They should not give the excuse that their mission is only to observe the ceasefire, because many massacres have been committed during their presence in Syria."

U.N. diplomats said they expected Annan to present the Security Council with a new proposal to rescue his failing peace plan by creating a 'contact group' of world and regional powers.

Some rebel groups, which have helped escalate what began as popular demonstrations for democracy into what is approaching a civil war, have lost faith in any ceasefire calls and are calling for more foreign arms and other support.

Western leaders, wary of new military engagements in the Muslim world and especially of the explosively complex ethnic and religious mix that Syria represents, have offered sympathy but show no appetite for taking on Assad's redoubtable armed forces, which can call on Iran and Russia for supplies.

In Washington on Wednesday, the United States and Saudi Arabia, among dozens of mostly Western and Arab countries in the Friends of Syria working group, called for further economic sanctions against Syria including an arms embargo, travel bans and tougher financial penalties.

ISTANBUL MEETING

Separately, ministers and envoys from 15 countries and the European Union agreed at a meeting hosted by Turkey in Istanbul on Wednesday to convene a 'coordination group' to provide support to the opposition but left unclear what it may involve.

U.S. Secretary of State Hillary Clinton was among officials from Europe, Turkey and Arab states who discussed 'additional steps' including coordination on an 'effective and credible transition process' to lead to a 'democratic, post-Assad Syria,' a Turkish statement said, adding that the group would be represented at a meeting in Istanbul next week of Syrian rebels.

Clinton told the group that transition in Syria must include a full representative interim government that would pave the way for a full transfer of power in free and fair elections.

Annan hopes his new idea can prevent a total collapse of his plan for a truce and negotiated political solution, U.N. diplomats said.

The core of the proposal, diplomats said, would be the establishment of a contact group that would bring together Russia, China, the United States, Britain, France and key regional players with influence on Syria's government or the opposition, such as Saudi Arabia, Qatar, Turkey and Iran.

By creating such a contact group, envoys said, Annan would also be trying to break the deadlock among the five permanent council members that has pitted veto powers Russia and China against the United States, Britain and France and prevented any meaningful U.N. action on the Syrian conflict.

It would attempt to map out a 'political transition' for Syria that would lead to Assad stepping aside and the holding of free elections, envoys said. One envoy said the idea was 'vaguely similar' to a political transition deal for Yemen that led to the president's ouster.

The main point of Annan's proposal, they said, was to get Russia to commit to the idea of a Syrian political transition, which remains the thrust of Annan's six-point peace plan that both the Syrian government and opposition said they accepted earlier this year, but have failed to implement.

'LIFE SUPPORT'

While Russia has said repeatedly it is not protecting Assad, it has given no indication it is ready to abandon him.

Assad has proven to be a staunch Russian ally and remains a top purchaser of weapons from Russian firms, and diplomats say Moscow continues to reward him for his loyalty.

"The thought is one that we've had for a little while, which is that you need to bind Russia into some sort of transition strategy on Syria," a senior Western diplomat said.

An unnamed diplomat leaked further details of Annan's proposal to Washington Post columnist David Ignatius, who said that if the contact group agreed on a transition deal for Syria, it would mean 'Assad would presumably depart for Russia, which is said to have offered him exile'.

It was not immediately clear if the idea of Russian exile for Assad was something Annan was pushing or if it was Ignatius' speculation. The Post article said that another option for Assad would be to seek exile in Iran, Damascus' other staunch ally.

In what could be the first step toward the creation of Annan's contact group, Russian Foreign Minister Sergei Lavrov on Wednesday floated the idea of an international meeting on the Syrian crisis that would bring together the prime candidates for Annan's proposed contact group, including Iran.

Clinton, however, reacted coolly to including Iran, which she said was 'stage-managing' the Syrian government assault on the opposition that the United Nations says killed at least 10,000 people.

Before he addresses the Security Council, Annan will speak to the 193-nation General Assembly, along with U.N. Secretary-General Ban Ki-moon and Arab League chief Nabil Elaraby.

Separately, envoys said it was unclear if the council would agree to extend the 90-day mandate of the unarmed U.N. observer mission in Syria, which is increasingly at risk of attack. Its mandate expires in late July.