Syria has blamed up to 800 rebel fighters for the massacre that killed more than 100 people, nearly half of them children, in its most comprehensive explanation to date of the bloodshed.
The narrative starkly contradicted accounts of witnesses who blamed "shabiha" or the shadowy gunmen who operate on behalf of President Bashar al-Assad's regime.
The UN also said it had strong suspicions those pro-regime gunmen were responsible for much of the carnage last Friday in a cluster of villages known as Houla.
Facing international outrage over the killings, Damascus launched its own investigation into the deaths and announced that special prayers for the victims would be held at mosques across the country on Friday.
At a news conference on Thursday, Qassem Jamal Suleiman, who headed the government's investigation into the massacre, categorically denied any regime role.
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He said hundreds of rebel gunmen carried out the slaughter after launching a co-ordinated attack on five security checkpoints.
The aim, he said, was to frame the government and to ignite sectarian strife in Syria. "Government forces did not enter the area where the massacre occurred, not before the massacre and not after it," he said, adding that the victims were families who refused to oppose the government or carry arms.
Foreign Ministry spokesman Jihad Makdissi said the aim was to create sedition in Syria.
"There are people in dark rooms working night and day to target Syria ... and the way to do it is to ignite civil strife," he told reporters at the same news conference.
"They will not succeed." The Houla massacre was one of the deadliest incidents since the uprising against Assad's hardline regime started in March last year. Activists say about 13,000 have been killed in 15 months.
The area is still under attack. The government focused its shelling on Thursday on the Houla village of al-Tibeh.
The activist group Syrian Observatory for Human Rights reported that some residents fled to nearby towns and villages "fearing a new massacre" as the area again came under fire.
Persistent bloodshed despite a ceasefire agreement has raised pressure on the international community to act.
But Secretary of State Hillary Clinton laid out the clearest case yet for why the Obama administration is reluctant to intervene militarily in Syria even as the US expressed revulsion over the Houla killings.
Clinton said Russia and China would have to agree before the US and other nations engage in what could become a protracted conflict in support of a disorganised rebel force.
"We're nowhere near putting together any type of coalition other than to alleviate the suffering," Clinton told reporters on Thursday after meeting with top officials in Denmark, a key contributor to last year's NATO-led mission against Muammar Gaddafi in Libya.
Russia's continued support for Assad "is going to help contribute to a civil war", Clinton warned.
