A Syrian man, living in Lebanon, carries a picture of Syria's President Bashar al-Assad. REUTERS/Stringer

United Nations human rights investigators on Syria said on Tuesday that preparing prosecutions against war criminals should not be delayed until the end of the conflict, now entering its sixth year.

The U.N. Commission of Inquiry, which has documented atrocities committed by all sides in the war, has compiled a confidential list of suspects and begun providing judicial assistance to authorities investigating foreign fighters.

President Vladimir Putin announced on Monday that “the main part” of Russia’s armed forces in Syria would start to withdraw, telling his diplomats to step up the push for peace as U.N.-mediated talks resumed in Geneva between the Syrian government and opposition.

“Now for the first time, there is hope of an end in sight,” Paulo Pinheiro told the U.N. Human Rights Council as U.N.

Special Envoy Staffan de Mistura carried out mediation efforts nearby.

“The adoption of measures that lay the ground for accountability need not and should not wait for a final peace agreement to be reached,” Pinheiro told the forum, flanked by co-commissioners Carla del Ponte and Vitit Muntarbhorn.

Michael Ratney, U.S. Special Envoy for Syria, said: “The United States unequivocally condemns atrocities committed by all sides, but we must not forget what the Syrian people will always remember: Assad and his allies have been, from the very beginning, by far the primary source of killing, torture, and deprivation in this war.” Activists and the independent U.N. investigators are “all laying the ground work for holding perpetrators of crimes accountable in the future, Ratney said, adding: “It is not a question of if; it is a question of when.

“CRIMINAL JUSTICE”

Criminal justice is essential but currently the only justice referred is through national courts of member states. We will continue to call for referral to the ICC (International Criminal Court) or an ad hoc tribunal,” Pinheiro said.

But he also called for immediate steps to plan a long-term process of transitional justice and respect for rule of law.

Serious violations continue, with thousands detained and tortured, many dying in custody, he said. Islamic State (ISIS) – which is not part of the cessation of hostilities that went into force on Feb. 27 – continues to use suicide bombs and has more than 3,000 Yazidi women as sexual slaves, he added.

Pinheiro urged the government and opposition to agree to confidence-building measures. These included unconditional and immediate release of all prisoners arbitrarily detained – especially women and children – setting up a mechanism to trace those missing and an end to sieges.

“We are convinced this would lay a foundation to the beginning of a real transition,” he said.

Syrian Ambassador Hussam Aala said that rebel groups were targeting residential areas in Damascus and Aleppo with shelling and rockets, depriving civilians of water, and using medical facilities as command centres.

These “terrorist” groups were backed by Qatar, Turkey and Saudi Arabia, he said.

“The Syrian government continues to send relief to all areas in need without discrimination… We have been responsible in abiding by the cessation of hostilities in order to preserve Syrian blood,” he said.