Syria on Thursday blamed up to 800 rebel fighters for the massacre in central Syria last week that killed more than 100 people, nearly half of them children, The Associated Press reported.

The accusations starkly contradicted accounts of witnesses who blamed “shabiha”, the gunmen who operate on behalf of President Bashar Assad’s regime, for the massacre in the Houla region.

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 Thursday, Qassem Jamal Suleiman, who headed the government’s investigation into the massacre, categorically denied any regime role. He claimed that hundreds of rebel gunmen carried out the slaughter, after launching a coordinated attack on five security checkpoints.

The aim, he said, was to frame the government and to ignite sectarian strife in Syria, AP reported.

“Government forces did not enter the area where the massacre occurred, not before the massacre and not after it,” Suleiman 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 was quoted as having told reporters at the same news conference. “They will not succeed.”

A Houla-based opposition activist said it was clear that there had been no government investigation.

“The regime is looking for ways to justify the massacre to the world,” the activist, Saria al-Houlany, told AP. “It’s clear that there wasn’t any professional probe. … If we had 800 fighters in Houla, this massacre would not have happened.”

Earlier on Thursday, UN Secretary-General Ban Ki-moon warned against a civil war in Syria, 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. A united international community demands that the Syrian government act on its responsibilities to its people,” he added.

The rebels of the Free Syrian Army on Thursday gave President Bashar al-Assad until Friday noon to observe the UN-brokered plan to end bloodshed in the country. Otherwise, it warned, it will no longer be tied by any commitment to the ceasefire plan brokered by UN envoy Kofi Annan.

Meamwhile, British Foreign Secretary William Hague said he is working with partners in other European Union countries to impose additional sanctions on Syria, without the approval of the UN Security Council.