AMMAN (Reuters) - The gunmen arrived shortly before dusk, some in uniform and some in plain clothes, before herding whole families into rooms and killing them in cold blood, according to survivors.
"They entered our homes ... men wearing fatigues herding us like sheep in the room and started spraying bullets at us," said an apparently injured woman in a video released by activists.
"My father died and my brother, my mother's only son. Seven sisters were killed," the woman said, lying next to another injured woman and near a baby with a chest wound.
The United Nations says 108 people were killed in the May 25 massacre, nearly half of them children, outraging a world long numbed by 14 months of relentless bloodshed since the start of a popular uprising against Syrian President Bashar al-Assad.
The events are disputed. The West blames Assad's forces, while Syria accuses its opponents, whom it refers to as Islamist "terrorists".
But video footage and accounts of activists, survivors, rights groups and United Nations observers in Syria, provide a harrowing narrative of the violence in the Houla region, about 20 km (13 miles) northwest of the city of Homs.
Crucially, the U.N. monitors say the evidence appears to contradict the government's denial that its forces and allied militia were behind the slayings.
Activists and survivors said soldiers and pro-Assad "shabbiha" militiamen from the president's minority Alawite sect carried out the onslaught on the Sunni Muslim villagers.
"They are all shabbiha of Assad. They came to us from (the nearby villages of) Fela and Sharklia. They are Alawite pigs. They attacked us and said 'die you pigs' and left," said the unidentified woman in the video, swathed in a blanket and wearing a black headscarf.
It is far from the first mass killing in Syria. But the presence on the ground of U.N. monitors - and their forthrightness in describing it as a massacre of mostly women and children - has made the incident a potential turning point in the effort to galvanise international opinion against Assad.
U.N. human rights spokesman Rupert Colville said 49 children and 34 women were among those killed, while fewer than 20 people had died in bombardment.
"What is very clear is that this was an absolutely abominable event that took place in Houla, and at least a substantial part of it were summary executions of civilians - women and children," Colville said.
Like many confrontations in Syria, the violence began with protests against Assad's rule at Friday prayers in the village of Taldaou, and quickly spilled into bloodshed and clashes.
Activists said security forces fired on the demonstrators, killing several people. Free Syrian Army rebels attacked army checkpoints around the mainly Sunni villages of the Houla district, seizing control of at least one.
Up to five government armoured vehicles, including tanks, were damaged in the fighting, testimony to the increasing firepower at the rebels' disposal.
"In late afternoon, Taldaou came under heavy tank shelling and rocket fire," said activist Maysara al-Hilawi, who said he had witnessed Friday's events. "A number of people were killed, and the rebels withdrew."
He said shabbiha militiamen from outlying Alawite villages entered Taldaou at around 6 p.m., under covering army fire.
According to Hilawi and witnesses interviewed by Human Rights Watch, many of the killings occurred on the southern fringe of Taldaou on a road leading southwards to the Alawite villages and a dam.
Hilawi said he had ventured out into the streets of Taldaou at around 8.30 p.m. "I found lots of people massacred in their homes on the dam road leading to the Alawite villages.
"Those who tried to escape were machinegunned and the bodies of nine men and six women who ran away were found today among the farmlands. There are more bodies of victims near roadblocks which we cannot reach."
He said 63 people from a single extended family of Sunnis called Abdelrazzaq were killed in their houses.
"The shabbiha came back at 2.30 in the morning and killed more than 15 people from the al-Sayyed family in their houses. A baby, Ali Adel al-Sayyed, miraculously survived," Hilawi said, referring to another family of Sunnis.
Several videos of the aftermath show bloodied corpses of men, women and children.
"That's Firas," screams a man in one clip, turning over the corpse of a man whose skull appears to be partially detached, a thick pool of blood beneath him.
Other footage and pictures posted on the day of the killings showed a child with its throat slit, with what appear to be burn marks near what may be an entrance wound on the upper rib cage.
Another showed a girl, apparently shot in the right eye, blood soaking the right side of her clothing.
Western leaders expressing outrage over the killings have focussed on the plights of children. In another video circulated on the Internet, a child described what he said had happened.
"The soldiers came in. My mother started shouting at them for taking my brother and my uncles. They pointed their guns at her head and shot her five times," the boy said.
The boy said a soldier found his hiding place and shot at him, "but the bullet landed at my side."
"There were 11 of them - some in uniform and some civilians with shaved heads and beards - Shabbiha.... I left the house trembling, I saw the bodies of my sister, my mother and my brothers on the bed. I saw them all."
Syrian authorities restrict media access and it is impossible to verify videos posted by activists who seek to portray Assad's forces in the worst possible light. Some people shown in the videos appeared to have been prompted for their answers.
In a letter to the United Nations, the government denied any tanks had been in the area and said the killings bore the hallmarks of Islamist militants whom the government has long blamed for the violence in Syria. It said the victims had been chosen because they had publicly declared support for Assad.
That account challenged what U.N. Secretary-General Ban Ki-moon told the Security Council on Sunday, citing U.N. observers who saw artillery and tank shells, as well as fresh tank tracks, along with many buildings destroyed by heavy weapons.
The U.N. Human Rights Council in Geneva said most of the 108 dead were civilians and that witnesses and survivors had told U.N. investigators that most were victims of two bouts of summary executions carried out by shabbiha.
U.N. peacekeeping chief Herve Ladsous also said the weaponry used pointed to the army, and the shabbiha were "probably" responsible for the killings.
"Part of the victims had been killed by artillery shells. Now that points ever so clearly to the responsibility of the government. Only the government has heavy weapons, has tanks, has howitzers," he told reporters in New York.
"But there are also victims from individual weapons, victims from knife wounds and that of course is less clear but probably points the way to the shabbihas, the local militia," he said.
Additional reporting by Mariam Karouny and Joseph Logan; Writing by Dominic Evans; Editing by Alistair Lyon and Peter Graff