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The head of the UN has said monitors trying to reach the Syrian village of Qubair, where 78 people are said to have been killed, were fired upon.

None were hurt in the shooting but they have pulled back for the night.

Addressing the UN General Assembly, Secretary General Ban Ki-moon condemned the "killing of innocents" at Qubair as "shocking and sickening".

Envoy Kofi Annan told the UN Security Council the crisis could soon "spiral out of control", diplomats said.

Mr Annan earlier told the General Assembly his six-point peace plan was not being implemented despite having been accepted by Damascus.

Opposition activists blame the killings at Qubair on pro-government forces but the government accuses "terrorists".

The White House said it strongly condemned "the outrageous targeted killings of civilians including women and children" in Qubair.

But both China and Russia repeated their opposition to outside intervention in Syria.

The UN has 297 unarmed observers in Syria to verify the implementation of a peace plan negotiated by Mr Annan. It includes a ceasefire, meant to have taken effect in mid-April.

"I just learned a few minutes ago that while trying to [enter Qubair], the UN monitors were shot at with small arms," Mr Ban told the 193-state assembly in New York.

"Any regime or leader that tolerates such killing of innocents has lost its fundamental humanity," he said.

Addressing the special closed meeting of the Security Council later, Mr Ban gave several examples of how UN observers had narrowly escaped injury, a diplomat told the ´óÏó´«Ã½'s Barbara Plett.

"The secretary general mentioned to the Security Council a heavy weapons round landing near a patrol... and armour-piercing bullets fired at at least one vehicle," the official said.

A drone had also been spotted overhead on one occasion, the official said.

At the same session, Mr Annan urged world powers to warn President Bashar al-Assad of "clear consequences" if he did not comply with the six-point peace plan, diplomats said.

Sausan Ghosheh, spokesperson for the UN observer mission in Syria, told the ´óÏó´«Ã½ the monitors had been sent home for the night.

"We're here serving the flag of the United Nations... until now we're lucky no-one has been injured," she said.

Speaking earlier in Syria, UN mission chief Gen Robert Mood said Syrian troops had blocked access to Qubair, which is near the western city of Hama.

In a statement, the White House said the killings, coupled with the "Syrian regime's refusal to let UN observers into the area", were "an affront to human dignity and justice".

UK Foreign Secretary William Hague said the situation in Syria was "rapidly deteriorating" into sectarian violence.

China's envoy to the UN, Li Baodong, said: "We resolutely oppose the solutions to the Syrian crisis through outside armed intervention or any attempt to forcibly promote regime change."

The latest violence comes less than two weeks after 108 people were killed in a massacre in Houla.

Harrowing videos of dead children have been circulating on the internet purporting to show victims of the Qubair attack.

According to clandestine activists, security forces bombarded Qubair, about 20km (12 miles) north-west of Hama, late on Wednesday.

Qubair is a small farming settlement inside the Sunni Muslim village of Maarzaf, which lies close to Alawite villages.

Activists blamed much of the killing on local pro-government Alawite militiamen known as shabiha.

Militiamen allegedly shot and stabbed many people, with some bodies reportedly set alight along with houses.

The Local Co-ordination Committees, a network of activists, said 78 people had died in Qubair, including 35 members of one family.

Syria's ambassador to the UN, Bashar Jaafari, denied Syrian government involvement in the killings and said the allegations were mere propaganda and not helping the situation.

State TV reported that security forces had launched an attack on an "armed terrorist stronghold" in Qubair after appeals from citizens.

It said a UN observer team had entered Qubair and had "witnessed a crime by the terrorists, who killed nine women and children".

Members of the international community in Damascus say that most victims at Houla were killed by gunfire raking rooms and not in execution-style killings, contrary to initial reports.