Foreign extremists are escalating the conflict in Syria by joining the fighting in growing numbers, the UN commission investigating human rights abuses in the country warned Monday.
"Such elements tend to push anti-government fighters towards more radical positions," the panel's chairman, Paulo Pinheiro, said at the United Nations Human Rights Council in Geneva.
But the regime of Syrian President Bashar Assad has also been receiving foreign help. Iran's Revolutionary Guards, for instance, acknowledged providing such assistance for the first time on Monday.
Pinheiro did not specify where the foreign fighters were coming from. He said that some were fighting alongside the rebels, while others were operating independently.
"The commission confirmed the increasing presence of foreign elements, including Jihadist militants, in Syria," he reported.
He added that sectarian violence between Sunni Muslims on one side, and Shias and Alawites on the other, was also on the rise.
Pinheiro stressed that government forces and its allied militias had committed more serious war crimes and human rights violations than the rebels.
He highlighted daily indiscriminate attacks on civilians, as well as reports that in several areas trapped civilians are "barely managing to survive."
The panel also said they had drawn up a new secret list of Syrians and military units suspected of committing war crimes who should face criminal prosecution some day.
The independent investigators, led by Paulo Pinheiro, said they had gathered "a formidable and extraordinary body of evidence" and urged the UN Security Council to refer the situation in Syria to the International Criminal Court (ICC).
He did not say if any Syrian rebels, as well as officials, were named on the list, which updated a confidential one his team submitted to UN rights chief Navi Pillay in February.
"A second confidential list of individuals and units believed to be responsible for violations is being provided to the High Commissioner of Human Rights," Pinheiro told the UN Human Rights Council in Geneva.
Syrian ambassador Faysal Khabbaz Hamoui accused Western and Arab powers of sending funds and weapons to support rebels conducting what he called a jihad or holy war against Damascus, and warned that the plan would backfire.
"The mercenaries are a time bomb that will explode later in the country and in the countries supporting them after they finish their terrorist mission in Syria," he declared.
The report should have named countries that "support the killers", which he said included the United States, Qatar, Saudi Arabia, Turkey and Libya.
Ongoing fighting in restive areas, meanwhile, prevented some schools from opening on the second day of the new school year, activists said.
Since the early hours of the day, shelling targeted areas in Idlib and Aleppo. An amateur video posted online by activists showed horrific images of a man holding the body of a little girl who had been decapitated in the shelling.
The UN has estimated that more than 2,000 schools have been damaged or destroyed since the uprising in Syria began in March 2011.
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