Pro-Russian separatists vowed Monday to mobilise up to 100,000 fighters for their latest east Ukraine offensive as the US mulled sending weapons to Kiev's out-gunned forces after the latest truce bid collapsed.
The ambitious pledge to dramatically escalate a nine-month conflict that has already left at least 5,100 people dead came as the rebels battled to encircle beleaguered transport hub Debaltseve.
"There will be general mobilisation in the (separatist) Donetsk People's Republic in 10 days' time, we plan on mobilising up to 100,000 men," rebel leader Alexander Zakharchenko told the separatist news agency DAN.
Fighting in Ukraine's industrial heartland has intensified in recent days, with Kiev officials and local authorities saying Monday that five Ukrainian soldiers and three civilians had been killed in the last 24 hours.
Fighting in east Ukraine claimed around 50 lives over the weekend, as the latest attempt at truce talks collapsed in acrimony in Minsk on Saturday.
Ukrainian military spokesman Volodymyr Polyovyi in Kiev said Sunday that "constant battles" were going on around railway hub Debaltseve but pledged that government forces would not give up control of the last remaining road into the town.
- Lethal assistance
The surge in fighting comes as Washington and NATO's military commander appear to be moving towards supplying arms to Ukrainian forces, The New York Times reported Sunday.
President Barack Obama's administration was reviewing whether to provide "lethal assistance", in addition to non-lethal aid such as body armour and medical equipment which it already supplies to Kiev, it said.
"A comprehensive approach is warranted, and we agree that defensive equipment and weapons should be part of that discussion," a Pentagon official told the Times.
US Secretary of State John Kerry is set to jet into Kiev on Thursday to pledge Washington's support during talks with President Petro Poroshenko and Prime Minister Arseniy Yatsenyuk.
Western governments and Ukraine have accused Russia of sending regular troops and arms to bolster the rebels and spearhead the latest offensive -- claims Moscow has repeatedly denied.
The rebels, however, are equipped with the heavy weaponry of a regular army, hardware they claim to have captured from fleeing Ukrainian forces.
- 'Not prepared for truce' -
French President Francois Hollande, German Chancellor Angela Merkel and Ukrainian President Petro Poroshenko, speaking by phone on Sunday, expressed their regret for "the failure of the talks" in the Belarussian capital Minsk.
The three leaders again called for "an immediate ceasefire", according to the French presidency.
Mediators and Ukrainian representatives accused the separatists of scuppering Saturday's truce talks despite growing international pressure to end a surge in violence in recent days.
The Organization for Security and Cooperation in Europe (OSCE), which is involved in the talks along with Russia, said that rebel negotiators in Minsk "were not even prepared to discuss implementation of a ceasefire and withdrawal of heavy weapons".
Instead the insurgent representatives called for a total revision of an earlier Kremlin-backed peace plan signed in September that has formed the basis for all negotiations, the OSCE said in a statement.
The rebels say they now want to redraw the demarcation line between the two sides to include gains they have made since ripping up a shaky truce and pushing into Ukrainian territory.
The insurgents on Sunday slammed the OSCE for pinning the blame on them and said Kiev needs to halt fire before they will agree to a truce.
The 28-nation European Union last week 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.
But deep divisions within the EU meant that there was no agreement on expanding broad sanctions targeting Russia's economy.