* Pinheiro says team's next report will be "dreadful"
* Says increasingly difficult to define good or bad rebels
* Del Ponte says crimes worse than in Balkans wars
Most Syrian rebel fighters do not want democracy and the country's civil war is producing ever worse atrocities and increasing radicalisation, independent U.N. investigators said on Tuesday.
Speaking to reporters in Paris, Brazilian expert Paulo Pinheiro said his team of investigators had documented horrific crimes on both sides, although the scale of those committed by President Bashar al-Assad's forces was greater.
"It was said the rebels were angels, but there is only a minority of fighters with a democratic history who believe in the Syrian mosaic and want a state for all," he said.
"The majority of rebels are very far from having democratic thoughts and have other aspirations."
The U.N. Security Council is set to blacklist Syria's Islamist al-Nusra Front as an alias of al Qaeda in Iraq. Foreign fighters, many of them from Libya, Tunisia, Saudi Arabia, Lebanon, Iraq and Egypt, have also radicalised the rebels.
The Islamist element of the Syrian conflict poses a quandary for Western powers and their Arab allies, which favour Assad's overthrow, but are alarmed at the growing power of militant Sunni Muslim fighters whose anti-Shi'ite ideolgy has fuelled sectarian tensions in the Middle East.
While Assad has repeatedly labelled opposition forces as "terrorists", Western powers have backed non-Islamist rebel fighters by providing aid and non-lethal assistance.
On Monday, the European Union effectively lifted an arms embargo that could allow countries to arm certain rebel forces by failing to agree to renew it.
Pinheiro declined to comment on that decision, but suggested identifying groups acceptable to the West was difficult.
"There is a very complicated distinction between the bad and the good rebels," he said.
Pinheiro leads an independent team of some two dozen experts mandated by the United Nations that documents crimes committed during the conflict, in which at least 80,000 people have been killed.
Its next report is due out on June 4 and will be based on interviews since February conducted abroad with victims and witnesses, as they have not been allowed into Syria.
"The report is dreadful in terms of a combination of secularisation, radicalisation and an escalation in violations of human rights and laws of war," he said.
Both government forces and armed rebels are committing war crimes, including killings and torture, spreading terror among civilians in the more than two-year conflict.
Carla Del Ponte, a former Swiss attorney general who served as prosecutor of the International Criminal Tribunal for the former Yugoslavia and is one of four commissioners on the team, said she had never seen violence like that in Syria.
"The crimes are committed by both sides," she said. "The cruelty of these crimes is unbelievable. I have never seen that, not even in Bosnia."