To Russia's expressed displeasure, Ukraine took a historic step toward NATO on Tuesday in a parliamentary vote, ahead of talks on ending the ex-Soviet state's separatist war.
Lawmakers in the government-controlled chamber overwhelmingly adopted a bill dropping Ukraine's non-aligned status - a classification assumed by states that refuse to join military alliances and thus play no part in wars.
President Petro Poroshenko had vowed to put Ukraine under Western military protection after winning an election called in the wake of the February ouster in Kiev of a Moscow-backed president. "European and Euro-Atlantic integrations - that is Ukraine's single course," Poroshenko tweeted moments after the 303-8 vote.
Ukraine assumed de facto neutrality under strong Russian pressure in 2010. It had sought membership of the North Atlantic Treaty Organisation in the early post-Soviet era, but with its once-mighty army in ruins and riven by corruption, it was never viewed as a serious candidate.
Last winter's revolution in Kiev upset Russian President Vladimir Putin's plans to enlist Ukraine in a new bloc he was forging in order to counterbalance NATO and the European Union.
And Moscow had set Kiev's exclusion from all military unions as a condition for any deal on ending the pro-Russian uprising that has killed 4,700 in the eastern Ukrainian rustbelt in the past eight months.
Putin's view of NATO as modern Russia's biggest threat has only been reinforced by this year's dramatic spike in East-West tensions over Ukraine.
Russian foreign minister Sergei Lavrov demanded that Kiev "put an end to confrontation" and stop adopting "absolutely counterproductive" measures that only stoked tensions between the two sides.
Prime Minister Dmitry Medvedev said even more bluntly that "in essence, an application for NATO membership will turn Ukraine into a potential military opponent for Russia."
Medvedev warned that Ukraine's rejection of neutrality and a new Russian sanctions law that US President Barack Obama signed on Friday "will both have very negative consequences. And our country will have to respond to them," he wrote in a Facebook post.
Perhaps the most immediate threat will be to delicate peace talks this week in the Belarussian capital Minsk that Poroshenko and Putin agreed on Monday.
The deal for Kiev and rebel negotiators to meet in the presence of Russian and European envoys on Wednesday and Friday was struck during a joint call with German Chancellor Angela Merkel and French President Francois Hollande - the West's top mediators on Ukraine.
The last two rounds of Minsk consultations in September produced a truce and the outlines of a broader peace agreement that gave the two separatist regions partial self-rule for three years within a united Ukraine.
But the deals were followed by more fighting that killed at least 1,300 people. The insurgents' decision to stage their own leadership polls in violation of the Minsk rules effectively ended political talks between the two sides.
A new meeting in Belarus had been hampered by Kiev's refusal to discuss lifting last month's suspension of social security and other benefit payments to the rebel-run districts. Ukraine's leaders suspect the money is being stolen by militias in the Russian-speaking Lugansk and Donetsk regions and used to finance their war.
A Kiev-based representative for the Organisation for Security and Co-operation in Europe (OSCE) who will attend Wednesday's meeting said the sides will discuss humanitarian aid deliveries but steer clear of the payments debate.
The OSCE's Heidi Tagliavini added that the other big points on the agenda included the details of a mutual troop withdrawal and a prisoner exchange.
But Donetsk rebel representative Andrei Purgin said his side would insist on raising the funding issue - should the Minsk talks go ahead as planned.
Donetsk separatist envoy "Denis Pushilin is on his way to Minsk. But we still do not know if there will be negotiations tomorrow," Purgin told AFP by telephone.
Lugansk separatists said their envoy had also departed for Belarus for what they described as preparatory talks.
Self-declared Lugansk leader Igor Plotnitsky said he would personally attend a second meeting in Belarus on Friday should the sides agree the terms of a deal that met the rebels' main demands.