United Nations war crimes investigators on Syria say lower-level perpetrators should be prosecuted by foreign authorities until senior military and political figures can be brought before international justice.
The UN Commission of Inquiry, which has documented atrocities committed by all sides, has compiled a confidential list of suspects and maintains a database with 5000 interviews.
It has begun providing judicial assistance abroad in some cases.
Russian warplanes began leaving Syria on Tuesday as Moscow started to draw down forces that have tipped the war President Bashar al-Assad's way.
UN envoy Staffan de Mistura said he hoped the move would have a positive impact on peace talks under way in Geneva to end a conflict now in its sixth year.
"The adoption of measures that lay the ground for accountability need not and should not wait for a final peace agreement to be reached," Paulo Pinheiro, chief of the inquiry panel, told the UN Human Rights Council.
Carla del Ponte, a former UN war crimes prosecutor serving on the team, told reporters that it had received about 15 requests for information from various countries.
The cases involved low to middle-level perpetrators or foreign fighters.
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"It is a start towards international justice," she said.
Michael Ratney, US Special Envoy for Syria, condemned atrocities committed by various sides, but added: "Assad and his allies have been, from the very beginning, by far the primary source of killing, torture, and deprivation in this war."
Perpetrators of crimes will be held accountable, he said, and "it is not a question of if, it is a question of when".
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