
The UN human rights chief said on Thursday that Russian strikes on critical infrastructure in Ukraine since October had killed at least 77 civilians and were plunging millions of people into extreme hardship.
Much of the country remained without heat or power after the most devastating Russian air strikes on its energy grid so far. Since early October, Russia has launched missiles roughly once a week in a bid to destroy the Ukrainian power grid.
Moscow acknowledges attacking basic infrastructure but denies it targets civilians, saying it aims to reduce Ukraine's ability to fight and push it to negotiate. Kyiv says such attacks are a war crime.
"Millions are being plunged into extreme hardship and appalling conditions of life by these strikes," said Volker Turk in a statement. "Taken as a whole, this raises serious problems under international humanitarian law, which requires a concrete and direct military advantage for each object attacked."
In the same statement, he said the UN's preliminary analysis of videos that appeared to show Ukrainian soldiers executing Russian prisoners of war indicated they were "highly likely to be authentic". Kyiv has previously said it would investigate any alleged abuses by its armed forces.
The UN's monitoring team has said that both Russia and Ukraine have tortured prisoners of war.
Turk called on both Russia and Ukraine to issue clear instructions to their forces about the treatment of prisoners of war and said all allegations of summary executions should be investigated fully.
Ukraine's President Volodymyr Zelenskiy on Friday called on Europeans to remain united against Russia's war and to severely limit the price for Russian oil.
"There is no split, there is no schism among Europeans and we have to preserve this. This is our mission number one this year," Zelenskiy said in an address via a live video link to a conference in Lithuania.
"Europe is helping itself. It's not helping Ukraine to stand against Russia, this is helping Europe to stand against Russian aggression", he added.
European Union governments remained split on Thursday over what level to cap Russian oil prices at to curb Moscow's ability to pay for the war, and Zelenskiy called on the EU leaders to settle on the lowest proposal of $30.
"The price cuts are very important. We hear about (proposals to set the cap per barrel at) $60 or $70. Such words sound more like a concession (to Russia)", Zelesnkiy said.
"But I'm very grateful to our Baltic and Polish colleagues for their proposals, quite reasonable ones, to set this camp at $30 per barrel. It's a much better idea", he added.
The EU states failed to reach a deal on the price level for Russian sea-borne oil on Wednesday because a Group of Seven nations (G7) proposal for a cap of $65-70 per barrel was seen as far to high by some and too low by others.
Poland wants the cap to be set at $30, arguing that with Russian production costs that some estimate at $20 per barrel, the G7 proposal would allow Moscow too much profit. Lithuania and Estonia back Poland.