The United Nations’ top human rights official warned Friday that all-out civil war could engulf Syria unless countries that have backed international envoy Kofi Annan’s peace plan rally around calls for an independent probe into the killing of more than 100 civilians last week.

As countries lined up at an emergency meeting of the U.N. Human Rights Council to express their horror about the Houla massacre, in which the global body said 49 children were among the dead, the U.N. High Commissioner for Human Rights appealed for support for the six-point plan to halt the violence in Syria.

“Otherwise, the situation in Syria might descend into a full-fledged conflict and the future of the country, as well as the region as a whole could be in grave danger,” Navi Pillay told the 47-nation council in a speech read out on her behalf.

It was the fifth time that the Geneva-based Council called an urgent meeting on Syria, something the country’s ambassador to the U.N. in Geneva, Fayssal al-Hamwi, said was a sign that some countries are trying to divide his country.

Mr. al-Hamwi, too, condemned the massacre in Houla but blamed it on “groups of armed terrorists” seeking to ignite sectarian strife.

U.S. Ambassador Eileen Chamberlain Donahoe said there was no doubt that the regime of President Bashar Assad was responsible for the killing.

“There needs to be justice and accountability for those that committed these atrocities,” she told the council.

A draft resolution proposed by Qatar, Turkey and the United States condemns the killings in Houla and states that “those responsible for serious violations of human rights must be held accountable,” but doesn’t suggest how.

European diplomats want the resolution to include a call for the U.N. Security Council in New York to consider referring the massacre to the International Criminal Court. This is something the rights council cannot do on its own. And since Syria isn’t a member of the ICC, under international law only the Security Council can refer it to the Hague-based tribunal.

“Mostly we are pressing for some stronger language on accountability,” said Maria Ulff Moeller, a Danish diplomat whose country currently holds the rotating presidency of the European Union. “We can encourage the Security Council to refer the situation to the ICC, and it’s something we are pushing for.”

Other nations including the United States have been sceptical about invoking the International Criminal Court. But Ms. Donahoe indicated that information collected by the rights council’s investigators could be used for an ICC probe.

“We believe our role at the Human Rights Council is to provide the basis for a case that would be brought on crimes against humanity,” she told reporters in Geneva. “This would provide a basis for the Security Council to refer the matter to the ICC.”

The draft resolution also calls on Syria to allow the rights council’s panel of experts to visit the country, something it has previously rejected.

The head of the panel, Brazilian professor Paulo Sergio Pinheiro told Brazil’s O Estado de Sao Paulo newspaper on Thursday that “Houla is a warning of how a civil war would be.”

“The Syrians think that by impeding our access we won’t be able to make it, but we have proven that we can do it,” he was quoted as saying.

Meanwhile, a different U.N. expert panel tasked with investigating allegations of torture worldwide said Friday it was deeply concerned at widespread and systematic violations of international law by Syrian authorities, often using militias known as Shabiha. The panel said its conclusions are based on “consistent, credible, documented and corroborated allegations.”

Among the violations it cited are large-scale attacks, killing and torture of civilians including many women and children, summary executions, mass graves, sexual violence, secret detentions and arbitrary arrests.

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