Beirut: More than 90 civilians, including 32 children under the age group of 10, have been killed in the last 24 hours in the town of Houla, said opposition activists, describing the killings as a "massacre".
The head of a UN mission, Maj-Gen Robert Mood described the killings as "indiscriminate and unforgivable" and also warned of civil war.
"The circumstances that led to these tragic killings are still unclear," Mood told reporters.
"Those using violence for their own agendas will create more instability, more unpredictability and may lead the country to civil war," he added.
The Britain-based Syrian Observatory for Human Rights and the Local Coordination Committees activist groups said Syrian troops using tanks, mortars and heavy machine guns pounded the area of Houla, a region made up of several towns and villages in the province of Homs.
They said scores were wounded in the violence in Houla.
That death toll is one of the highest for any single event since the popular uprising against Bashar Assad began in March 2011.
Meanwhile, UN Secretary General Ban Ki-moon has said that "established terrorist groups" are suspected in many deadly attacks in the country, where the overall situation remains "extremely serious".
The UN chief also expressed disappointment over the lack of progress in bringing peace to the troubled nation despite efforts by UN-Arab League envoy Kofi Annan to broker peace between the warring government and opposition forces.
"We announce that unless the UN Security Council takes urgent steps for the protection of civilians, Annan`s plan is going to go to hell," the rebel Free Syrian Army (FSA) statement said.
An amateur video posted online by activists showed more than a dozen bodies lined up inside a room. They included about 32 children who were covered with sheets that only showed their bloodied faces.
"Houla was subjected to a massacre," a man could be heard saying inside the room.
The Observatory said in one incident in Houla, a family of six was killed when their home received a direct hit.
Homs has been among the hardest hit provinces in a government crackdown since the uprising against President Bashar Assad`s regime began in March last year. The UN said several weeks ago that 9,000 people have been killed in Syria in the past 15 months. Hundreds more have died since.
Attacks like Friday`s, as well as strikes by rebel forces on government troops, have persisted despite the deployment of more than 250 UN observers who have fanned out across Syria to monitor a ceasefire brokered by international envoy Kofi Annan.
The Syrian government has blamed the deaths on armed terrorist gangs.
Despite the daily violations, Ban Ki-moon said on Thursday that there was no "plan B" for the Annan initiative.
(With Agency inputs)