Syria's ambassador to the United Nations rejected the world body's estimate that 5,000 people have died in an uprising against the government, calling the allegation "incredible."
Ambassador Bashar Jaafari was responding to a briefing by U.N. Commissioner for Human Rights Navi Pillay, who told the Security Council Monday the situation in Syria was "intolerable."
She said more than 200 people had died in the last 10 days and "the Syrian population continues to live in fear of further violent repression."
The same day that Pillay spoke, the London-based Syrian Observatory for Human Rights and a resident of Homs -- an opposition hotbed and frequent site of violence in recent months -- reported that a gas pipeline exploded near the city, following by gunfire and circulating military airplanes.
The state-run Syrian Arab News Agency, or SANA, played up local elections Monday as an expression of "democracy and free will." Yet the Homs resident said there was no evidence of voting in that city. Instead, this witness reported nonstop shooting and bombardments.
The Syrian government, meanwhile, has consistently blamed the violence on "armed terrorist" gang members and denied any efforts to target peaceful civilians.
CNN cannot independently confirm events because the Syrian government restricts access of international media to the country.
Pillay said Monday that "the nature and scale of abuses" indicate that Syrian forces likely committed "crimes against humanity." Citing reliable sources, she said more than 300 of the dead have been children "killed by state forces."
Several defectors from military and security forces said they got orders "to shoot unarmed protesters without warning," according to Pillay.
"Independent, credible and corroborated accounts demonstrate that these abuses have taken place as part of a widespread and systematic attack on civilians," she said.
Homs has been a regular flash point. As nightfall arrived Monday, many city residents went to bed afraid the steady waves of violence could soon give way to a historic siege.
Opposition figures said the Syrian government had warned people in Homs to stop anti-government protests, hand in weapons and surrender defecting military members by Monday night -- or face attack by government forces.
Syrian forces gave a 72-hour warning, said Lt. Col. Mohamed Hamdo of the Free Syrian Army, an opposition group of defected Syrian military personnel. Activists on the ground said the ultimatum was issued Friday for Homs.
The government has not acknowledged any deadline for Homs in state-run media, and it was not clear Tuesday morning what had happened in the city overnight.
The Syrian government denied reports of water and electricity being out in the city, according to a SANA report.
The last nine months have seen a steady stream of clashes, amid reported government push-back against activists demanding democratic elections and the end of al-Assad's regime. Al-Assad has been in power since 2000; his father ruled Syria for three decades.
World leaders and diplomats have widely condemned Syria's crackdown and called on it to halt violence against the opposition.
The Arab League announced it will hold emergency meetings this week in Cairo. In a statement on Egypt's state-run MENA news agency, an Arab League official said leaders will "discuss the Arab response to a message from Syrian Foreign Minister Walid Moallem to approve the signing of an agreement on an Arab League observing mission to Syria with conditions."