United Nations war crimes investigators called on Tuesday for the establishment of a special tribunal to prosecute cases of mass atrocities in Syria, and said they had begun to share evidence and names of suspects with state and international prosecutors.

The UN commission of inquiry said it would still like the UN security council to refer the Syrian conflict to the international criminal court (ICC) for prosecutions. But after four years of war and over 220,000 dead, and in the face of continued Russian and Chinese opposition to an ICC referral, the commission said it was looking at other means to bring a measure of justice for mass crimes committed in Syria.

One of the commissioners, Carla Del Ponte, was the former chief prosecutor of the international criminal tribunal for former Yugoslavia (ICTY), created to investigate the Balkan conflicts in the 90s. She said that the ICTY example showed that an ad-hoc tribunal could eventually work in Syria.

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“At the beginning I was for the ICC but now with the changing situation, I think an ad-hoc tribunal could be more efficient and work faster,” Del Ponte told the Guardian in an interview in Geneva. “First of all, the ICC would prosecute only three, four, five perpetrators, not more. I think an ad-hoc tribunal could prepare a list of over a hundred, like the tribunal for the former Yugoslavia ... An ad-hoc tribunal could also be based near the region, facilitating access of witnesses, documentation and so on.”

A resolution being drafted by the UK and due to be presented to the UN human rights council next week calls for the commission to brief the UN general assembly on its findings and for the assembly in turn to present its reports to the security council. The move is intended to increase international pressure on China and Russia by demonstrating an international consensus behind war crimes prosecutions.

Del Ponte suggested that Russia, which has been a staunch ally of the Assad regime, could be more amenable to a special tribunal on Syria than a ICC referral, as a tribunal would be able to handle more cases. That would mean it would pursue more prosecutions of atrocities carried out by extremist elements of the opposition as well as members of the regime. The Swiss former prosecutor said she was ready to travel to Damascus herself to gather information and to talk to the regime, if the Syrian government confirmed she was still welcome.

Facebook Twitter Pinterest Members of the commission of inquiry on Syria, Karen Koning Abuzayd (L-R), Switzerland’s Carla Del Ponte, chairperson Brazilian Paulo Pinheiro, and Thailand’s Vitit Muntarbhorn, deliver a press conference in Geneva. Photograph: Salvatore di Nolfi /EPA

The UN commission of inquiry said last month that it would publish the secret list of its war crimes suspects, but it stopped short of taking that step on Tuesday. Instead, it said it had started sharing evidence, including names of suspects, with national prosecutors and judiciaries which are considering launching their own investigations.

Up to now, the state prosecutors it has cooperated with have been investigating the role of their own citizens in atrocities carried out by Islamic State or extremists among the opposition. However, another commissioner, Vitit Muntarbhorn, said the commission would also share evidence with national prosecutors pursuing cases under universal jurisdiction, by which national courts can try cases involving crimes against humanity or large-scale war crimes committed elsewhere.

“At this moment, we are not going to release the lists publicly,” Muntarbhorn said. “However ... we are open to cooperating with state authorities, particularly prosecution and judicial authorities, where they are investigating crimes and prosecuting alleged perpetrators. We are hoping to cooperate in terms of sharing some information in terms of incidents and alleged perpetrators on a confidential basis.”

“But there has to be a written request,” he added. “Those states would have to have independent, impartial judiciaries and to show respect for human rights.”