US Secretary of State John Kerry has begun talks in Geneva with his Russian counterpart to end fighting in Ukraine, where the UN said the death toll has soared past 6,000 people in less than a year.
The meeting with Sergei Lavrov in an upscale Geneva hotel on Monday came less than a week after Kerry accused Moscow of lying to his face about its involvement in the conflict, which has triggered the worst post-Cold War crisis between the US and Russia.
High-stakes talks between Kiev and Moscow were also set to get under way in Brussels to resolve a bitter gas dispute which threatens deliveries to Europe, after Russia began direct supplies to parts of separatist-held eastern Ukraine.
As relative quiet held on Ukraine's frontlines, raising hopes that Kiev and pro-Russia rebels holding parts of the east were moving towards implementing a shaky ceasefire, the UN published a report that painted a bleak picture of developments in the country.
"More than 6,000 lives have now been lost in less than a year due to the fighting in eastern Ukraine," UN High Commissioner for Human Rights Zeid Ra'ad Al Hussein said in a statement released with the report.
The report details how the conflict is affecting civilians, including arbitrary detention, torture and disappearances, committed mainly by armed groups but also in some cases by Ukrainian law enforcement agencies.
The swelling violence and dire living conditions have forced more and more people to flee, and by mid-February, at least one million people had been registered as internally displaced inside Ukraine.
'Crime against humanity'
Speaking in Geneva for the launch of the report, UN Assistant Secretary-General for Human Rights Ivan Simonovic said "the deliberate targeting of civilian areas may constitute a war crime and if widespread and systematic, a crime against humanity".
The dire comments coincided with the meeting between Kerry and Lavrov in Geneva, which was expected to focus on efforts to implement the ceasefire that began on February 15.
Both sides have also begun to pull back some heavy weaponry from the frontline, with rebels claiming on Sunday that they would complete the pullback by the end of the weekend.
Monitors from the Organization for Security and Co-operation in Europe have reported weapons movements on both sides but say it is too early to confirm a full pullback.
Kerry was expected to warn Lavrov that the US and EU are already working on another slew of sanctions - on top of the ones already slapped on Moscow - if it does not adhere to the new ceasefire deal, US officials said.
He was also due to press Lavrov to ensure that Moscow carries out a credible investigation into the assassination of Russian opposition leader Boris Nemtsov.