The meeting with Sergei Lavrov in an upscale Geneva hotel 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 its allies, 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-Kremlin rebels holding parts of the east were moving towards implementing a shaky ceasefire, the United Nations 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 ninth on the issue.
'Crime against humanity'?
The report details how the conflict is affecting civilians, including arbitrary detention, torture and enforced 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.
"Many have been trapped in conflict zones, forced to shelter in basements, with hardly any drinking water, food, heating, electricity or basic medical supplies," Zeid said.
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 shaky ceasefire that began on February 15th.
Ukraine security spokesman Andriy Lysenko said eight soldiers were injured after rebels shot at Kiev's positions late Saturday, including from a tank and a grenade launcher.
Journalists also mourned the killing by mortar fire of Ukrainian photographer Sergiy Nikolayev.
But in an encouraging sign, Kiev security officials said Sunday no Ukrainian soldiers had been killed over the past 24 hours.
Both sides have also begun to pull back some heavy weaponry from the frontline, with rebels claiming Sunday that they would complete the pullback by the end of the weekend.
Monitors from the Organization for Security and Cooperation 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
Meanwhile, not far away in Brussels, three-way gas talks were also set to take place between the energy ministers of Ukraine and Russia, together with European Commission vice-president Maros Sefcovic.
Russian state-owned gas giant Gazprom threatened last week to cut deliveries to Ukraine over a dispute related to Moscow's move to supply gas directly to separatist areas and then demand that Kiev pay for it.
Rebel leaders in east Ukraine said that Kiev had suddenly ceased gas supplies, and asked for access to gas from Russia.
Ukraine's national gas company Naftogas did stop pumping gas to the separatist areas last month, saying it could not deliver due to a damaged
pipeline, but added that deliveries resumed a few hours later.
Russian President Vladimir Putin has accused Ukraine of perpetrating a kind of "genocide" by denying energy to four million people living in territories hit by a humanitarian crisis.
The Kremlin appeared to soften its rhetoric, however, after the European Union unveiled plans last week for a continent-wide single energy market, with the goal of decreasing its reliance on Russian gas.