United Nations experts warned today that an increasing number of "foreign elements" including jihadis are now operating in Syria.
An independent UN panel gave its first report saying that outside terrorists have joined a war which is spiralling out of control. Some of these forces are joining armed anti-government groups while others are operating on their own.
"Such elements tend to push anti-government fighters towards more radical positions," panel head and Brazilian diplomat Paulo Sergio Pinheiro warned.
The panel accused both government forces, pro-regime militias and anti-government armed groups of war crimes and crimes against humanity including murder, execution, torture, arbitrary arrest, sexual violence and abuse of children.
Mr Pinheiro said that the human rights situation has "deteriorated to such a degree that it is difficult to describe in a few words.
"Gross violations of human rights have grown in number, in pace and in scale."
He said the frequency of these "egregious violations" were such that his panel could no longer investigate them all.
"Civilians, many of them children, are bearing the brunt of the spiralling violence," he said.
Syrian authorities have long blamed the anti-government uprising that began in March 2011 on foreign influence.
Syrian UN ambassador Faysal Khabbaz Hamoui contested the report's overall accuracy and objectivity.
But he agreed with Mr Pinheiro on the presence of outside elements, telling the council that "many international parties are working on increasing the crisis in Syria."