Kiev representatives and pro-Russian separatists finally met on Saturday to thrash out a "binding" truce despite Ukraine suffering one of its bloodiest days yet in the nine-month conflict with 15 troops killed.
Ukrainian police officers stand during a ceremony in Kharkiv on January 30, 2015, before their departure to the east of the country to take part in the "Anti-Terrorist Operation"
Mediators from the Organization for Security and Cooperation in Europe as well as Russian officials joined the delayed talks in the Belarussian capital Minsk after a nominal September ceasefire collapsed under the latest wave of violence.
The talks came as Ukrainian forces suffered their highest one-day loss since the September truce, with 15 soldiers killed and 30 wounded, said Defence Minister Stepan Poltorak.
OSCE officials said they hoped for a "binding" truce that would also provide for the "unrestricted supply of basic goods and humanitarian assistance" as the civilian death toll mounts in rebel regions Donetsk and Lugansk.
Former Ukrainian president Leonid Kuchma, the OSCE's Heidi Tagliavini, and separatist representatives Denis Pushilin and Vladislav Deinego, as well as Russian ambassador to Kiev Mikhail Zurabov, were participating in the talks aimed at defusing fighting that has left at least 5,100 people dead.
Pro-Kremlin Ukrainian business tycoon and politician Viktor Medvedchuk -- a close ally of Russian President Vladimir Putin who Moscow have backed as a mediator -- was also present at the talks.
The insurgents last week pulled out of peace talks and announced the start of an offensive designed to expand their control over a much broader swathe of the industrial southeast.
They said Friday they would push their offensive "until the entire Donetsk and Lugansk regions are freed" of Ukrainian troops should the talks fail.
- Key town 'surrounded' -
At least 24 people were killed in fighting on Friday, with Grad rocket attacks on the separatists' self-proclaimed capital Donetsk continuing late into the night, an AFP correspondent said.
Fighting is raging around the strategic Ukrainian-controlled transport hub of Debaltseve, some 50 kilometres (35 miles) northeast of the rebel stronghold of Donetsk.
The town of 25,000 people was built around a railroad connecting the two rebel centres of the Russian-speaking southeast.
Defence Minister Poltorak for the first time said that separatist forces had taken "partial" control of Debaltseve, where rebels claim to have surrounded some 8,000 Ukrainian troops.
The rebels on Friday said that they had taken the town of Vuglegirsk -- some 10 kilometres from Debaltseve -- although Ukrainian military spokesman Andriy Lysenko said fighting there was ongoing.
Both towns are without water, electricity or heating, said regional police chief Vyacheslav Abroskin.
The latest violence has alarmed Ukraine's Western allies, with US Secretary of State John Kerry announcing plans to express his support for the war-torn nation during talks in Kiev on Thursday with President Petro Poroshenko and Prime Minister Arseniy Yatsenyuk.
Kerry will then meet his Russian counterpart Sergei Lavrov on the sidelines of a security conference in Munich, the State Department said.
Western governments and Ukraine accuse Russia of arming and training the rebels, who are deploying extensive weaponry including tanks and multiple rocket launchers. Russia denies claims it has sent regular troops and arms to bolster the rebels, who claim to get all their weaponry from captured Ukrainian supplies.
The 28-nation EU on Thursday extended through September a first wave of targeted sanctions it had slapped on Moscow and Crimean leaders in the wake of Russia's March seizure of the Black Sea peninsula from Ukraine.
Russia accuses the West of manipulating the Ukrainian government, which came to power in elections after the ouster in huge street demonstrations last year of a Kremlin-backed leader.