Calls for Western military action against Syria intensified on Saturday after grisly footage of the bodies of children killed in fresh violence laid bare the failure of the United Nations-brokered peace plan.

In one of the bloodiest incidents to date in the 15-month long uprising, 92 people were killed after a 12-hour regime assault on Houla, in the central province of Homs.

Anti-government activists claimed that troops had first shelled several villages and then sent in gangs of pro-regime thugs to “massacre” local families in their houses.

Amateur videos released on YouTube showed footage of the mangled bodies of 14 child victims lying in rows in a makeshift morgue set up at a local mosque.

In one horrific scene, a man held up the limp corpse of a boy aged around seven years old, a gaping hole where the child’s nose and mouth should have been. “This child, what did he do to deserve this?” he screamed.

Unarmed UN monitors, who had reportedly been prevented from visiting the area on Friday because of the fighting, were reduced to documenting the attack’s horrific aftermath when they finally reached the scene on Saturday afternoon.

Major General Robert Mood, the UN mission chief in Syria, said that of the 92 bodies his staff had counted in Houla, at least 32 were “under the age of 10”. He described it as a “brutal tragedy”.

The bloodshed, which began on Friday and was reported to have continued into the small hours of Saturday morning, was amongst the worst single incidents since the popular uprising against President Bashar al-Assad began 15 months ago. It was also a severe blow to the credibility of the UN-backed peace plan that was supposed to introduce a ceasefire in early April. Critics said it was clear that the plan, backed by 250 UN monitors on the ground, was already in tatters.

On Saturday the Foreign Secretary, William Hague, called for an urgent session of the UN Security Council to discuss the killings, placing the blame squarely on the Syrian government.

“There are credible and horrific reports that a large number of civilians have been massacred at the hands of Syrian forces in the town of Houla, including children,” he said.

“The Assad regime must ensure full and immediate access to Houla and other conflict areas in Syria for the UN monitoring team, and cease all military operations.”

However, the main Syrian rebel coalition, the Free Syrian Army (FSA), said it was time for the international community to overcome its reluctance to get directly involved in the conflict, and to carry out strikes on regime forces.

The Friends of Syria group, which includes the United States, France, Britain, Germany and Saudi Arabia, has previously ruled out such action because of the risk of getting embroiled in what many fear is already a low-level civil war.

But General Mustafa Ahmed al-Sheikh, head of the Turkey-based FSA military council, said regime opponents had lost all faith in the UN Security Council, on which Damascus has Russia as a powerful backer. “We are calling urgently on the Friends of Syria to create a military alliance, outside of the UN Security Council, to carry out targeted strikes against Assad’s gangs and the symbols of his regime,” Mr Sheikh said.

Houla, a loose collection of villages with a population of about 40,000, lies on a plain around 25 miles north-west of the city of Homs, itself the subject of a brutal siege by President Assad’s forces in February.

The settlement is home mainly to members of Syria’s Sunni Islam majority, but borders areas dominated by President Assad´s minority Alawite sect.

While eyewitness reports of Friday’s violence were confused and often contradictory, it followed an anti-government demonstration in Houla after Friday’s midday prayers. Some claimed that rebel gunmen had earlier courted trouble by opening fire on checkpoints manned by government troops.

Whatever the spark, the scale of the ensuing attack appears to have been brutal even the standards of the Assad regime.

Mousab Azzawi, of the Syrian Network of Human Rights, told The Sunday Telegraph: “The operation started about midday, with the use of about 50 or 60 mortar shells. Then they started to use tanks and heavy artillery for two hours. After that they deployed about 13 or 14 cars with mounted guns, and raided houses at random. They took people out and started shooting indiscriminately.”

In one household, he claimed, the gunmen slaughtered two entire families, ranging from grandfathers to children.

“They did not kill them immediately by shooting. But they cut their throats with knives. That is a very worrying signal, that the regime is trying the maximum they can to push the people to a civil war.”

One local eyewitness, who gave his name only as Mohammed, added: “At about 7pm on Friday, a lot of Shabiha (pro-regime militiamen) came from three nearby Alawite villages. They killed some kids by knife, some by gun and some by suffocation. I saw with my eyes dozens of bodies of women and children.”

In video footage shot in the local mosque, a shaking camera panned over the children’s corpses, which were laid shoulder to shoulder and included some who looked under five years old.

In a corner, more corpses of men and women lay under patterned blankets, including what was said to be one entire family. “We’re being slaughtered like sheep here,” said one voice.

“Where are the UN observers?” pleaded another.

It was claimed that the majority of casualties had been inflicted at close quarters, rather than by shelling.

Chaotic scenes followed when the group of UN observers finally arrived in Houla on Saturday.

“The people begged the observers to come with them to evacuate the bodies,” said Maysara Al-Hennawi, another resident. “They refused to help us and they said that we should negotiate with the regime, and then they left.”

Thousands of locals took advantage of the presence of the observers to flee the area, he added, making their way through fields and rivers. The Syrian government also broadcast footage of the casualties, blaming them instead on “armed terrorist” groups which it said had also killed several government troops. Damascus has long accused activist groups of exaggerating and falsifying accounts to draw international attention to their plight, a charge which independent observers say has sometimes been justified. There seemed little doubt about the veracity of the video footage of the corpses in the latest incident, though, which surfaced amid reports that Kofi Annan, the former UN secretary general, was to visit Damascus this week to try to patch up the ceasefire.

On Saturday, one demonstrator in Houla held up a sign reading: “Kofi Annan is single-handedly responsible for the Houla massacre.”

The scale of the task facing Mr Annan was spelt out in a report leaked on Friday from the current UN secretary general, Ban Ki-moon, which conceded that rebel groups now controlled “significant” parts of some Syrian cities and that there was “considerable physical destruction” across the country.

“There is a continuing crisis on the ground, characterised by regular violence, deteriorating humanitarian conditions, human rights violations and continued political confrontation,” said the report, which is to be debated by the Security Council this week.

More than 12,600 people are now estimated to have died in Syria in the revolt against Mr Assad’s rule, including nearly 1,500 since the UN-backed truce officially come into effect, according to the Observatory for Human Rights.

In a sign that the regime’s grip on the country was slipping further, tanks were deployed by the government for the first time this weekend in Aleppo, Syria’s second largest city. The city, a key commercial hub, had previously been considered a pro-regime bastion, but saw large street protests on Friday.

While neither side in the struggle is really seen to have properly observed the ceasefire, the Free Syrian Army on Saturday warned that unless there was an immediate halt to regime violence, it would abandon any commitment to it at all. “We announce that unless the UN Security Council takes urgent steps for the protection of civilians, Annan’s plan is going to go to hell,” a statement read.

The group’s calls for foreign military intervention are currently opposed at the highest level. Only last week, however, the UN explicitly urged foreign states not to supply arms to either the government or rebel forces.

“Those who may contemplate supporting any side with weapons, military training or other military assistance, must reconsider such options to enable a sustained cessation of violence,” UN secretary-general Mr Ban told the Security Council in a letter on Friday. Additional reporting by Richard Spencer and Magdy Samaan in Cairo (© Copyright of Telegraph Media Group Limited 2012. 05/27/12)