Updated 5:39 a.m. ET Sunday: The perpetrators of a massacre that left more than 92 dead – including 32 young children – in Houla, Syria “must be identified and held to account," Secretary of State Hillary Clinton said Sunday.

The United Nations said the victims died in what activists described as an artillery barrage by government forces in the worst violence since the start of a peace plan to slow the flow of blood in Syria's uprising.

The bloodied bodies of children, some with their skulls split open, were shown in footage posted to YouTube purporting to show the victims of the shelling in the central town on Friday. The sound of wailing filled the room.

Clinton issued a statement early Sunday saying the United States condemned the attack “in the strongest possible terms”. She also issued a warning for the country's leader, President Bashar Assad.

“Those who perpetrated this atrocity must be identified and held to account,” she said. “And 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.

“We stand in solidarity with the Syrian people and the peaceful marchers in cities across Syria who have taken to the streets to denounce the massacre.”

British Foreign Secretary William Hague said he was coordinating a "strong response" to the killings and would call for the U.N. Security Council to meet in the coming days. 

Activists said Assad's forces shelled  Houla after security forces killed a protester and following skirmishes between troops and fighters from the Sunni Muslim-led insurgency fighting Syria's rulers, who belong to the minority Alawite sect.

However, Syrian authorities denied responsibility. "Women, children and old men were shot dead. This is not the hallmark of the heroic Syrian army," the country's foreign ministry spokesman Jihad Makdesi told reporters in Damascus on Sunday, according to Reuters.

Earlier, Syrian state television aired some of the footage disseminated by activists after the killing, calling the bodies victims of a massacre committed by "terrorist" gangs.

The carnage underlined just how far Syria is from any negotiated path out of the 14-month-old revolt against Assad. 

Reuters

These were among the bodies being prepared for burial in Houla, Syria, on Saturday.

The U.N. first reported the massacre on Friday. "The observers confirmed from examination of ordinances the use of artillery tank shells," Maj. Gen. Robert Mood said in a statement, without elaborating. "Whoever started, whoever responded and whoever carried out this deplorable act of violence should be held responsible."

The UK-based Syrian Observatory for Human Rights said residents continued to flee the town, in central Homs province, in fear that artillery fire would resume.

Syria calls the revolt a "terrorist" conspiracy run from abroad, a veiled reference to Sunni Muslim Gulf powers that want to see weapons provided to an insurgency led by Syria's majority Sunnis against Assad, a member of the minority Alawite sect.

The U.N. says more than 9,000 people have been killed, most of them civilians, in the uprising. 

Reuters and The Associated Press contributed to this report.

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Updated 1:07 p.m. ET: As Syrian forces shelled the battered city of Homs through Saturday morning, the United Nations Security Council authorized the deployment of 30 unarmed observers to the country.

The military observers have been tasked with monitoring a tenuous cease-fire that began three days ago. Syrian activists said the cease-fire, called for by former U.N. Secretary General Kofi Annan, was ignored by the Syrian military.

The first group of observers was on stand-by, ready to fly to Syria when the council gave the green light, according to Reuters. 

Saturday’s resolution states that if Syria does not cooperate, the council would “assess the implementation of this resolution and to consider further steps as appropriate,” Reuters reported. 

The council reached the resolution after a 24-hour debate with Russia, according to The New York Times. It is the first resolution the 15-nation council, including China and Russia, has approved since uprisings began in Syria more than a year ago. Moscow and Beijing have twice vetoed similar council resolutions reprimanding Syrian President Bashar al-Assad.

Russia's ambassador to the UN made it clear that Russia would support only limited UN action, the Guardian of London reported.

On Friday, Syrian forces used live fire, tear gas and clubs to beat back thousands of protesters who took to the streets across the country in often jubilant displays of defiance, The Associated Press reported. It was the first use of force since the cease-fire began.  

The BBC reported 750 rallies, stretching from the suburbs of Damascus, the Syrian capital, to the central province of Hama, Idib in the north and southern province of Daraa, where the uprisings began in March 2011. Six people were killed.

Syrians take to streets in test of truce

"Come on, Bashar, leave!" the crowd shouted in Daraa, linking arms and stomping their feet to the beat of a drum in a traditional Arab folk dance, The AP reported, citing a video posted online by activists.

McCain, Lieberman demand Syrian rebels be armed

"We tried our best to reach Assi Square in order to show the world the truth about the regime -- they are lying and will not allow us to have big, peaceful demonstrations," Mousab Hamadee, an activist in that city, told the BBC. "As we approached Assi Square, they started opening fire on us. Two of my colleagues were martyred." 

Reuters and Associated Press contributed to this report.

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Armed forces loyal to Syrian President Bashar Assad on Saturday bombarded the Jobar residential neighborhood of Homs, where a standoff continued between a Red Cross convoy and the government that has blocked the delivery of food, medical supplies and blankets to the thousands still stranded in the area.

Thousands of civilians from another area overrun by the army have taken refuge in the neighborhood, an opposition activist organization said.

"In an act of pure revenge, Assad's army has been firing mortar rounds and ... machine guns since this morning at Jobar. We have no immediate reports of casualties because of the difficulty of communications," the Syrian Network for Human Rights said in statement.

Jobar is adjacent to the district of Baba Amr in Homs, from where Free Syrian Army rebels pulled out this week after almost a month of army shelling. Activists reported mass executions by loyalist troops who subsequently entered the area.

The Local Coordination Committees activist network said mortars slammed into Khaldiyeh, Bab Sbaa and Khader districts of the city early Saturday.

Graphic: The siege of Homs

Abu Hassan al-Homsi, a doctor at a makeshift clinic in Khaldiyeh district of Homs, said he treated a dozen wounded.

"This has become routine, the mortars start falling early in the morning," he said. Several homes were damaged from the morning shelling, which he described as steady but intermittent. Most of those he treated were lightly wounded, al-Homsi added.

Aid convoy blocked
The International Committee of the Red Cross (ICRC) said Saturday it was still negotiating with Syrian authorities who have denied its aid convoy access to the shattered Baba Amr district.

An ICRC convoy of seven trucks carrying food and other life-saving relief supplies, joined by Red Crescent ambulances to evacuate the sick and wounded, has been stalled in the city of Homs since arriving there on Friday.

Red Cross convoy prevented from entering former Syrian rebel stronghold

"The ICRC and Syrian Red Crescent are not yet in Baba Amr today (Saturday). We are still in negotiations with authorities in order to enter Baba Amro. It is important that we enter today," ICRC spokesman Hicham Hassan told Reuters in Geneva.

ICRC President Jakob Kellenberger, in a statement issued on Friday after waiting all day for Syrian authorities to grant entry to the team, said the delay was "unacceptable" as civilians had waited for weeks for emergency assistance.

U.N. Secretary-General Ban Ki-moon said on Friday he had received "grisly reports" Syrian government forces were arbitrarily executing, imprisoning and torturing people in the battle-scarred city of Homs after rebel fighters had fled.

PhotoBlog: The fear of carnage to come

'Terrorist' suicide bombs
Meanwhile, the Syrian state news agency Sana reported Saturday that a suicide bomber killed two people and wounded several others in the southern town of Deraa.

"The terrorist explosion led to the martyrdom of two citizens," the agency said.

The British-based Syrian Observatory for Human Rights also reported that at least two people were killed and several others wounded in the explosion.

Syrians flee to northern Lebanon

Syria has seen a string of suicide bombings, the last on Feb. 10, when twin suicide bombs struck security compounds in the government stronghold city of Aleppo, killing 28 people and bringing significant violence for the first time to the city.

The capital Damascus, another stronghold of Assad's, has seen three suicide bombings in the past two months.

The regime has touted the attacks as proof that it is being targeted by "terrorists." The opposition accuses forces loyal to the government of being behind the bombings to tarnish the uprising.

Saturday's bombing in Deraa marked the first time a suicide bombing struck an opposition stronghold. Daraa is the birthplace of the nearly year-old uprising against Assad. The revolt has killed more than 7,500 people, according to most recent U.N. estimates.

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Reuters and The Associated Press contributed to this report.