Civilians in eastern Ukraine are facing increasing hardships, with wrecked infrastructure and limited access to power and water supplies, the UN says.
UN humanitarian chief John Ging said "immediate action" was needed to halt the conflict and prevent the situation from putting more people in danger.
At a UN Security Council meeting Russia blamed Ukraine for the hardships, but the UK said it was Russia's fault.
More than 1,500 people are believed to have been killed since April.
The crisis erupted when well-armed pro-Russian gunmen took over various cities and attempted to break away from Ukraine.
They have been slowly beaten back, and the fighting is now focused on the two rebel strongholds of Donetsk and Luhansk.
Heavy fighting once again erupted on Tuesday in a suburb of the rebel stronghold of Donetsk.
Read more: http://www.bbc.co.uk/news/world-europe-28669764