"They are good candidates for the list," Paulo Pinheiro said, referring to public executions and crucifixions carried out by the terrorist group in Syria.

The confidential list was revealed to the UN Security Council and reporters for the first time on Friday.

The foreign-sponsored Takfiri terrorists, who control vast swathes of territory in northern Syria and neighboring Iraq, have been engaged in fierce fighting against Syrian government forces in Raqqa province in recent days.

"I can assure you that we are collecting information on perpetrators from all sides including non-state armed groups and ISIS," said Brazilian native Pinheiro, the head of the independent UN commission on Syrian war crimes in a press conference.

UN human rights investigator Karen Koning Abu Zayd has also warned that more and more Syrian insurgents were defecting from their own foreign-backed groups to join the extremist ISIL terror group because they are thought to be better finance and stronger.

Meanwhile, the ISIL terrorists said on Friday they had seized control of a large military base on the outskirts of the northern city of Raqqa.

They released images of captured soldiers being beheaded after the battle for the base, the largest of its kind in the north-east of Syria.

The UN Commission of Inquiry on Syria was set up in September 2011 in order to collect witness accounts, satellite photographs and other information documenting human rights violations throughout the conflict.

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