Up to 16 civilians have been killed and dozens more injured in the space of 24 hours in fighting in eastern Ukraine, as the UN warns that the fresh surge in violence is proving "catastrophic".
Government and rebel representatives reported the latest deaths in locations across the Donetsk and Luhansk regions.
Ukraine's army also said five soldiers had died fighting pro-Russian rebels near the strategic town of Debaltseve.
Civilian casualties have risen sharply in recent weeks amid a rebel offensive.
The latest deaths were in the city of Donetsk, Debaltseve and several villages under government control in the Luhansk region. The exact numbers could not be independently confirmed.
'Bus stop battlegrounds'
UN human rights chief Zeid Ra'ad Al Hussein said there had been a "clear breach of international humanitarian law which governs the conduct of armed conflicts".
"Bus stops and public transport, marketplaces, schools and kindergartens, hospitals and residential areas have become battlegrounds in the Donetsk and Luhansk regions of Ukraine," he said in a statement.
"Any further escalation will prove catastrophic for the 5.2 million people living in the midst of conflict in eastern Ukraine," he added.
According to the UN, the death toll now exceeds 5,350 people and more than 12,000 other people have been wounded in the fighting.
There has been heavy fighting around Debaltseve, site of a key railroad junction, for the past week, with rebels trying to surround government forces.
The BBC's David Stern in Kiev says reports suggest there is a growing humanitarian crisis in the town, which is virtually cut off by the battle.
A Ukrainian journalist who visited told the BBC that Debaltseve had been virtually destroyed and many residents were trapped - hiding in basements, without food, electricity or water supplies.
In another development, the government in Kiev announced new rules limiting the documents that Russians can use to enter Ukraine, a move correspondents say will increase tensions with Moscow.
From 1 March, Russians will need an external passport to gain entry to Ukraine rather than just their internal identity documents, a government decree said.
Some 1.2 million have fled their homes since last April, when the rebels seized a big swathe of Luhansk and Donetsk regions, following Russia's annexation of Crimea.
The latest casualty figures come amid fears that the fighting in eastern Ukraine is escalating.
On Monday, pro-Russian separatist leader Alexander Zakharchenko said rebels were aiming to boost their forces to 100,000 men.
Ukraine's government has also announced a major mobilisation, with plans to bring the numbers in its armed forces to 200,000 by later this year.
Meanwhile, US officials are reported to be considering sending defensive weapons and other lethal aid to Ukraine's armed forces.
Nato says the rebels are being supported by hundreds of Russian tanks and armoured vehicles that have crossed the border into eastern Ukraine.
The Kremlin has denied direct involvement but says some Russian volunteers are fighting alongside the rebels.
Ukraine's war: The human cost
- 5,358 people killed and 12,235 wounded in eastern Ukraine
- Fatalities include 298 people on board flight MH17 shot down on 17 July
- 224 civilians killed in three-week period leading up to 1 February
- 5.2 million people estimated to be living in conflict areas
- 921,640 internally displaced people within Ukraine, including 136,216 children
- 600 000 fled to neighbouring countries of whom more than 400,000 have gone to Russia
Are you in the Donetsk or Luhansk regions? Have you been affected by recent events? You can email email@example.com with your experience.
Please include a telephone number if you are willing to be contacted by a BBC journalist.