When the gunmen began to slaughter his family, 11-year-old Ali el-Sayed says he fell to the floor of his home, soaking his clothes with his brother's blood to fool the killers into thinking he was already dead.

The Syrian boy tried to stop himself from trembling, even as the gunmen, with long beards and shaved heads, killed his parents and all four of his siblings, one by one.

The youngest to die was Ali's brother, six-year-old Nader. His small body bore two bullet holes —one in his head, another in his back.

"I put my brother's blood all over me and acted like I was dead," Ali told The Associated Press over Skype on Wednesday, his raspy voice steady and matter-of-fact, five days after the killing spree that left him both an orphan and an only child.

Ali is one of the few survivors of a weekend massacre in Houla, a collection of poor farming villages and olive groves in Syria's central Homs province. More than 100 people were killed, many of them women and children who were shot or stabbed in their houses.

The killings brought immediate, worldwide condemnation of President Bashar Assad, who has unleashed a violent crackdown on an uprising that began in March 2011. Activists say as many as 13,000 people have been killed since the revolt began.

UN investigators and witnesses blame at least some of the Houla killings on shadowy gunmen known as shabiha who operate on behalf of Assad's government.

The regime denies any responsibility for the Houla killings, blaming them on terrorists. And even if the shabiha are responsible for the killings, there is no clear evidence that the regime directly ordered the massacre in a country spiralling toward civil war.

According to the UN, which is investigating the attack, most of the victims were shot at close range, as were Ali's parents and siblings. The attackers appeared to be targeting the most vulnerable people, such as children and the elderly, to terrorize the population.

By most accounts, the gunmen descended on Houla from an arc of nearby villages, making the deaths all the more horrifying because the victims could have known their attackers.

Ali, the 11-year-old, said his mother began weeping the moment about 11 gunmen entered the family home in the middle of the night. The men led Ali's father and oldest brother outside.

"My mother started screaming 'Why did you take them? Why did you take them?"' Ali said.

Soon afterward, he said, the gunmen killed Ali's entire family.

As Ali huddled with his youngest siblings, a man in civilian clothes took Ali's mother to the bedroom and shot her five times in the head and neck.

"Then he left the bedroom. He used his flashlight to see in front of him," Ali said. "When he saw my sister Rasha, he shot her in the head while she was in the hallway."

Ali had been hiding near his brothers Nader, 6, and Aden, 8. The gunmen shot both of them, killing them instantly. He then fired at Ali but missed.

"I was terrified," Ali said, speaking from Houla, where relatives have taken him in. "My whole body was trembling."

Ali is among the few survivors of the massacre, although it was impossible to independently corroborate his story. The AP contacted him through anti-regime activists in Houla who arranged for an interview with the child over Skype.

Days after the attack, many victims remain missing.

Ali can describe the attack on his family. But al-Qassem said the full story of the massacre may never emerge.

"There are no eyewitnesses of the massacre," he said. "The eyewitnesses are all dead."