The leaders of France, Germany, Russia and Ukraine have begun talks to resolve the conflict in Ukraine, while pro-Russia separatists tighten the pressure on Kiev by launching some of the war's worst fighting.
As talks got under way in Belarus on Wednesday, Ukraine's army said 19 of its soldiers were killed in rebel assaults near the railway town of Debaltseve.
Rebels who tore up a five-month-old truce in January are trying to encircle government forces in Debaltseve, a strategic location that would let them link up their main strongholds.
RELATED: Russia stands firm as Minsk talks begin
Fighting has already killed more than 5,000 people, and Washington is now openly talking of arming Ukraine to defend itself from "Russian aggression", raising the prospect of a proxy war in the heart of Europe between Cold War foes.
A surge in fighting in the 24 hours before the summit, including a rocket attack that killed 17 people in government-held territory on Tuesday, could be intended to force Ukraine to accept a deal recognising the rebel advance.
The summit was being held in neighbouring Belarus under a French-German proposal to try to halt the fighting. German Chancellor Angela Merkel and French President Francois Hollande began talks with Ukraine's Petro Poroshenko and Russia's Vladimir Putin.
The leaders were planning to sign a joint declaration supporting Ukraine's territorial integrity and sovereignty, a Ukrainian delegation source said.
The source said a separate document would be prepared by a "contact group" of Russia, Ukraine and the Organisation for Security and Cooperation in Europe affirming commitment to a ceasefire plan drawn up in Minsk last September and also signed by separatist leaders.
The comments were a partial read-out from the Ukrainian side and with the summit starting in earnest it was too early to say what compromise, if any, had been worked out between Ukraine and Russia.