LOS ANGELES, CA (Catholic Online) - Video images of bloodied, young bodies laid out in a shallow grave after last week's onslaught triggered shock around the world. The atrocity underlined the failure of a six-week-old U.N. cease-fire plan to stop the violence.

Fewer than 20 of the victims died from artillery fire, the U.N. High Commissioner for Human Rights declared. It was first thought the majority of the deaths were caused by artillery fire.

Syrian authorities have long blamed "terrorists" for the massacre. Houla was among the worst carnage in the 14-month-old uprising against Assad, which has cost about 10,000 lives.

The U.S. has rejected Syria's claims that terrorists were responsible for the massacre.

"We hold the Syrian government responsible for this slaughter of innocent lives," a spokesman for State Department said in a statement. "We encourage all countries to condemn the actions of the Assad regime through similar action."

The U.S. has not severed all diplomatic relations with Syria altogether. U.S. officials say that they did not oppose "many civil service members of the Syrian government who are working to improve their country."

Spokesman for the UNHCR Rupert Colville told the journalists in Geneva that initial investigations suggest fewer than 20 of the victims in the village of Taldou, near Houla, were killed by artillery or tank fire.

"Most of the rest of the victims in Taldou," he told the BBC, "were summarily executed in two separate incidents." He added that most of the victims were shot at close range. "At this point it looks like entire families were shot in their houses," Colville was quoted as saying.

He said the conclusions of the U.N. monitors are corroborated by other sources, and that witnesses blamed pro-government militias for the attacks.

The findings came as U.N.-Arab League envoy Kofi Annan was meeting President Bashar Assad in Damascus this week.

The U.N. Security Council on Sunday unanimously condemned the Syrian government for heavy-weapons attacks on Houla.

"The Security Council condemned in the strongest possible terms the killings, confirmed by United Nations observers, of dozens of men, women and children and the wounding of hundreds more in the village of (Houla), near Homs, in attacks that involved a series of government artillery and tank shellings on a residential neighborhood," a non-binding statement said.

U.S. Secretary of State Hillary Clinton demanded that those responsible for the massacre be brought to justice.

"The United States will work with the international community to intensify our pressure on Assad and his cronies, whose rule by murder and fear must come to an end," she said.

© 2012, Catholic Online. Distributed by NEWS CONSORTIUM.