Conflict at 'crossroads' after troop deaths

International monitors said the conflict in Ukraine was at a "crossroads" as further losses among government forces rattled a two-week-old truce just as it seemed to be gaining traction.

The deaths of three Ukrainian soldiers after a two-day lull in clashes with pro-Russian separatists highlighted the fragility of the ceasefire as the United Nations said some five million people needed humanitarian aid due to the conflict.

The envoy to Ukraine for the Organisation for Security and Cooperation in Europe (OSCE), which is monitoring the peace deal, told the UN Security Council that while there were encouraging signs, the country still risked all-out war.

"We seem to be at the crossroads, where we are facing the risk of a further escalation of the conflict or where common sense, responsibility, and humanity shall prevail and we may be able to walk on the road to peace," envoy Heidi Tagliavini told the 15-member council.

The Security Council's meeting on the conflict came a year to the day after Russian and pro-Moscow forces began occupying strategic sites on the Black Sea peninsula of Crimea.

Russia formally annexed the territory in March 2014, triggering an international furore. The uprising in Ukraine's east began the following month.

The UN said on Friday there was a crisis in rebel-held areas, where people were living in "extraordinarily difficult circumstances".