A Syrian government investigation determined that security forces had nothing to do with the Houla massacre and blamed the act on terrorists, officials said Thursday.
The massacre, which left more than 100 people dead last weekend, sparked outrage across the globe and prompted loud calls for action against the Bashar al-Assad regime.
But Syria attributed the latest violence to "armed terrorist groups," the vague entities that the regime has blamed all along for violence during the nearly 15 months of unrest.
"The goal of the armed operation was to completely terminate the presence of the state in the area and to make it one that is out of the control of the state," Qasim Jamal Sleiman, head of the investigative panel, said in remarks aired on television.
"All of the martyrs are from peaceful families who refused to stand against the state and have never demonstrated or carried weapons against the state. They were in disagreement with the armed terrorist groups, which confirms that there was a goal and an interest to kill them."
The U.S. ambassador to the United Nations, Susan Rice, called the Syrian account "another blatant lie" and said there's no "factual evidence" to "substantiate that rendition of events." She said the U.N. Human Rights Council in Geneva, Switzerland, could soon embark on an effort to establish facts in the case and hold people accountable.
The Syrian government investigation said about 600 to 800 armed people gathered after Friday prayers at two main points and committed the crimes. Sleiman said firearms from a close distance and sharp objects were used, but there was no shelling.
"The place where the massacre was committed is an area where armed terrorist groups are present. The security forces did not enter the area before or after the massacre and the area is far from the checkpoints where the security forces are positioned," Sleiman said.
But he said security forces "defended themselves against the armed terrorist groups."
Some of the attackers hailed from the Houla area, investigators said. "Also, some of the bodies that were shown as part of the massacre are bodies of armed individuals who were killed during their attack on the security forces and they are not from the town."
Politicians across the world, opposition leaders and Syrian citizens blame the regime, citing witness accounts that pro-government forces were responsible for the Houla bloodshed. They say government forces have been responsible for violence in Syria since March 2011.
The massacre spurred concerted diplomatic action this week. The United States, Netherlands, Australia, Britain, France, Germany, Italy, Japan, Spain, Bulgaria, Turkey and Canada announced that they are expelling Syrian diplomats.
Rice has said the massacre was carried out by Shabiha militias or local gangs acting on behalf of the regime.
Survivors told Human Rights Watch that the army shelled the area and "armed men, dressed in military clothes, attacked homes on the outskirts of town and executed entire families."
A network of Syrian opposition activists, the Local Coordination Committees of Syria, blamed "armed militias" of the Syrian government.
"This barbaric act was preceded by the regime's mortar shelling in the town," the LCC said in a statement. "The campaign ended when the armed militias slaughtered entire families in cold blood."
Sectarian tensions have been high in Houla, which is overwhelmingly Sunni and is surrounded by Alawite and Shiite villages. The regime is dominated by Alawites.
Syria has repeatedly denied involvement but promised the investigation.
The government report comes as U.S. Secretary of State Hillary Clinton ramped up pressure on Russia Thursday, saying the Kremlin has been an obstacle to forging peace in Syria.
"I think they are, in effect, propping up the regime at a time when we should be working for transition," Clinton told reporters in Denmark on Thursday.
The United States and Russia have been among the world powers involved in looking for solutions to the 15 months of persistent violence in Syria. The violence has left thousands dead, with death estimates ranging from more than 9,000 to more than 14,000.
Along with other world powers, the United States is focused on supporting U.N. and Arab League envoy Kofi Annan's six-point peace plan. The administration is hoping Russia can persuade Syrian President Bashar al-Assad to adhere to the plan and keep the country from deteriorating into more warfare.
The Syrian regime said it supported the Annan plan, which includes a cease-fire. But so far, according to the secretary of state, the Syrian regime has failed to abide by every point in the initiative.
"The Russians keep telling us they want to do everything they can to avoid a civil war because they believe the violence will be catastrophic" and they have likened the situation to the "equivalent of a very large Lebanese civil war," Clinton said.
"They're just vociferous in their claim that they are providing a stabilizing influence," she said. "I reject that."
Clinton urged leaders in Syrian society and the military to use their influence to avoid a full-blown civil war. She said counties like the United States and Denmark are "appalled" by the violence and want "to win over those who still support the regime inside and outside of Syria to see what options are available to us."
"We're also aware that there is still a fear among many elements of the Syrian society and the Syrian government, that as bad as the Assad regime is, it could get worse," she said. "And we therefore continue to call upon the business leadership, the religious leadership, the military leadership, those voices within the government that know what is going on is leading to the very outcome they fear most -- which is a sectarian civil war -- to stand up now and call a halt to further support for this regime."
Clinton said the world regards the Houla massacre "with horror" and "those responsible must be held to account."
Merchants in Aleppo shut their stores to register their disgust with Houla on Thursday, echoing the same angry gestures last Monday in the historic Hamidiyeh Bazaar in downtown Damascus.
"We carry the responsibility for continuing to work while people are dying," said an Aleppo store-owner who asked to only be named Abu Karim, in a phone interview with CNN.
"That is our shame," Abu Karim said.
U.N. Secretary-General Ban Ki-moon referenced the Houla incident on Thursday in Istanbul, Turkey, saying "the massacre of civilians of the sort seen last weekend could plunge Syria into a catastrophic civil war -- a civil war from which the country would never recover."
"I demand that the government of Syria act on its commitments under the Annan peace plan," he said. "A united international community demands that the Syrian government act on its responsibilities to its people."
Russia and China have been more receptive to the Syrian government during the crisis, and have blocked tough action against the Assad regime in the U.N. Security Council.
Russian Foreign Minister Sergey Lavrov said earlier this week that "certain countries" were attempting to use the Houla massacre as a "pretext" for a military operation against al-Assad's forces, which have been partly armed by Russia, Russia's RIA Novosti reported.
Lavrov also accused the head of the opposition Syrian National Council of attempting to "incite a civil war." The government also said proposals by Western powers to arm rebels would "prolong the conflict."
Since the conflict began, the government has blamed the violence against civilians on armed terrorist groups. But opposition groups and citizens have said the government has fomented the discord.
Violence continued in Syria on Thursday, with at least 41 people killed in the country, the LCC said. Syrian forces shelled Houla again early in the day, it said, and the dead include 11 people executed in the Homs province city of Qosair.
CNN cannot confirm death tolls or reports of violence from Syria because the government limits access to the country by foreign journalists.
Syrian opposition fighters issued the government a Friday afternoon deadline to cease-fire, pull out troops from residential areas and allow humanitarian aid.
The Free Syrian Army, mainly comprised of military defectors, did not say what would happen if the government fails to comply.
"Our national, moral and humanitarian duty make it necessary for us to defend and protect our civilians and their cities, towns, blood and dignity," the group said in a statement.
The ultimatum lists a series of demands in a peace plan implemented last month and brokered by Annan.
"Immediately halting gunfire and all violence, pulling out all the troops, tanks and machinery from residential areas, allowing humanitarian aid to reach all stricken areas, releasing all prisoners and allowing media access," said Col. Qasim Saad Eddine, the group's spokesman.
Eddine also called for freedom to demonstrate, an end to attacks on U.N. monitors in the nation and a dialogue on power handover.
Meanwhile, Syrian authorities freed 500 prisoners arrested for their alleged involvement in the 15-month uprising against the government, state TV reported Thursday. No more information was immediately available.