The United States yesterday warned Russia it had only "hours" to prove it was helping disarm Ukrainian insurgents whose tenuous truce with Kiev was due to expire by the weekend.
US Secretary of State John Kerry stressed in Paris that "it is critical for Russia to show in the next hours, literally, that they're moving to help disarm the separatists, to encourage them to disarm, to call on them to lay down their weapons and to begin to become part of a legitimate process."
The ultimatum was delivered a day before Ukrainian President Petro Poroshenko signs the final chapters of an historic EU accord that nudges his country toward eventual membership and pulls it firmly out of Russia's reach.
The West is scrambling to save a temporary ceasefire and nascent peace talks that pro-Russian separatists who are now threatening the ex-Soviet state's survival agreed to at the start of the week.
The truce -- broken on repeated occasions but still having succeeded in tempering the worst of the violence in the Russified eastern rustbelt -- formally runs out today at 0700 GMT.
The Kremlin said Putin assured German Chancellor Angela Merkel shortly after Kerry's tough message that he fully backed a ceasefire's extension and resumption of meaningful dialogue between the warring sides.
The 11-week insurgency has killed more than 435 people and shattered the delicate system of trust that developed between Moscow and the West since the Cold War.
The US State Department added that sanctions would be also discussed by EU leaders yesterday when they sign the full Association Agreement with Ukraine that was ditched by the ousted pro-Russian president in November and now lies at the heart of the raging crisis.
The punitive steps under deliberation would target Russia's financial and defence sectors at a time when its export-dependent economy is on the verge of slipping into another recession.
US media reports said one particularly painful step under consideration would prohibit the export of technology that could help Russia explore for oil and gas in the Arctic -- a major ambition of powerful state-held energy firms.