The UN Commission of Inquiry on Syria says it is becoming increasingly difficult to access newly arrived Syrian refugees in European countries.
United Nations' war crime investigators have called upon European countries hosting Syrian refugees to improve access to help document fresh abuses.
It is becoming increasingly difficult to access newly arrived Syrian refugees in European countries, the UN Commission of Inquiry on Syria, told UN Human Rights Council.
"We are appealing to countries inside Europe hosting newly arrived Syrian refugees to grant us access and remove any barriers to our work," Paulo Pinheiro, chairman of the UN Commission of Inquiry on Syria said.
He said the UN Commission has compiled a confidential list of suspects on all sides that have committed war crimes or crimes against humanity.
He called again for major powers to refer Syria to the International Criminal Court.
Pinheiro did not name the European countries hampering investigators' access to Syrian refugees.
Most of the refugees have gone to Germany and Sweden while others remain stuck in Greece and Italy seeking asylum.
"Time is of the essence, particularly if the Commission is to continue preparing well-documented reports on the current situation in the country, rather than reports of a historical nature," Pinheiro said.
The UN Commission said earlier this month that it had a database of some 5,000 detailed interviews and information, some of which is being shared with European governments seeking to prosecute their nationals fighting as foreign militants in Syria.
"There have been cases of successful prosecution which our information has aided," Pinheiro told the 47-member Geneva forum on Monday, without elaborating.
Carla del Ponte, a panel member and former UN war crimes prosecutor, said:
A 20-truck aid convoy destined for the rebel-held eastern part of Aleppo with enough supplies to feed tens of thousands remains stuck in Turkey, UN officials said on Monday, hours after a seven-day Syria ceasefire agreed between the US and Russia ended.
Julian Braithwaite, Britain's envoy to the UN council, cited "clear evidence" of both Syrian regime forces and DAESH group killing civilians with chemical arms, making it crucial for UN investigators to hold perpetrators to account.
Moscow stepped up a war of words with Washington on Sunday, saying deadly air strikes by the US-led coalition on Syrian regime forces threatened the implementation of a US-Russian ceasefire plan.
Russia has backed Syrian regime leader Bashar al-Assad in the country's civil war while the US has supported the rebels fighting to topple him.