ISTANBUL: UN chief  Ban Ki-moon warned Thursday of a “catastrophic civil war” in Syria after the massacre of more than 100 civilians in the town of Houla that sparked global horror and outrage.

“The massacres of the sort seen last weekend could plunge Syria into a catastrophic civil war, a civil war from which the country would never recover,” he told an Istanbul forum of the UN-led Alliance of Civilisations initiative.

Ban's remarks came amid mounting international outrage over the massacre in the central town of Houla, in which at least 108 people, including 49 children, were killed, according to UN figures.

The assault prompted Western countries, including the United States, Britain, France, Australia to expel the senior Syrian diplomats in their countries.

The bodies from the Houla massacre were counted by UN observers whom Ban described as “our eyes and ears of the international community.”The observers were in Syria “so that perpetrators of crimes may be held accountable,” he said.

“We are not there to play the role of passive observer to unspeakable attrocities.”The UN chief demanded that the Damascus regime honour its commitment to a peace plan drawn up by international mediator Kofi Annan.

“I demand that the government of Syria act on its commitment to the Annan peace plan,” he said.

He also demanded that “the Syrian government act on its responsibilities to its people.”An international team led by Annan visited Syria Tuesday and called for “concrete gestures” from Damascus on halting the violence.

In Istanbul, Ban said: “Annan has expressed his concerns that we may have reached a tipping point in Syria.”The UN chief dismissed talk of a clash of civilisations between East and West over Syria.

“We hear a great deal about the so-called clash of civilisations, the supposed rift between predominantly Muslim and Western societies,” he said.

“This is not what is going on in Syria. There, it is the old story of a tyranny seeking to hold power.

“And in seeking to hold power, the regime threatens to exacerbate tensions among Syria's diverse people, much as we saw in the former Yugoslavia two decades ago.”

More than 13,000 people, mostly civilians, have been killed since an uprising erupted against President Bashar al-Assad's regime in March 2011, according to monitoring groups.