GENEVA (Reuters) - War crimes investigators and activists have amassed an “overwhelming volume” of testimony, images and videos documenting atrocities committed by all sides during Syria’s war, a U.N. quasi-prosecutorial body said in its first report.

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The team, led by former French judge Catherine Marchi-Uhel, said it is preparing case files and has engaged with war crimes investigative units of various states including in Europe, whose courts can exercise universal jurisdiction to prosecute.

In the future, an existing body - such as the International Criminal Court - or a new court could be given jurisdiction for Syria, according to the report.

The team expects to finaliZe an agreement soon with the Commission of Inquiry (COI) on Syria on getting access to testimony and evidence collected by that separate team of U.N. investigators for the past six years, the report said.

“The volume of videos and other images - as well as the role played by social media - is unprecedented in any other accountability process with respect to international crimes to date,” said the report by Marchi-Uhel’s team.

“...It is not possible to prosecute all of the crimes committed, given their vast number,” it added.

But there is a need to sure “fair representation” by prosecuting crimes committed on all sides, and sexual and gender-based crimes, as well as violations against children, will be a priority, said the report, released on Monday.

Investigators were also seeking to obtain information on the use of chemical weapons in Syria from the Organisation for the Prohibition of Chemical Weapons.

A COI report on March 15 said Syrian government forces and allied militias had raped and sexually assaulted women, girls and men in a campaign to punish opposition communities - acts that constitute war crimes and crimes against humanity.

Led by Paulo Pinheiro, the COI has accused Syrian government forces of committing war crimes and potentially crimes against humanity, including mass executions, and some opposition groups of international crimes such as murder and torture.

Marchi-Uhel’s team said its work would proceed independently of any Syrian peace process and be based on the principle that no amnesty can be granted for “core international crimes”.