Two days before the vote, Friday May 9, is the annual Victory Day holiday celebrating the Soviet Union's victory over Nazi Germany. Moscow has been openly comparing the government in Kiev to the Nazis, and Ukrainian officials say they are worried that the day could provoke violence. In Moscow, there will be a massive parade of military hardware through Red Square, a Soviet-era tradition revived by President Vladimir Putin.
The past few days have seen government forces press on with an offensive but make little progress in the east, where separatist rebels have so far held firm at their main outpost in the town of Slaviansk and shot down three Ukrainian helicopters.
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Interior Minister Arsen Avakov said on Tuesday more than 30 separatists had been killed in fighting around Slaviansk, but there was no confirmation of such a figure. The rebels, who triggered fighting in the area on Monday by ambushing government troops, said four of their number had been killed.
At roadblocks in the town, some armed fighters have been replaced by civilians, like Alexandra, in her late 20s, who said she leaves her 10-year-old daughter at home each morning, puts a starting pistol in her belt and walks to the barricades. The tactic of putting civilians at the front could make a government offensive more difficult.
"We have two options - to use heavy artillery ... wipe everything out, put the flag up and report that everything has been done. The second option is a gradual blockade, destroying provocateurs and sabotage to prevent injuries among the population. We are carrying out the second scenario," said acting defence minister Mykhailo Koval, explaining why the operation has taken so long and achieved so little.
Since a pro-European government took power after the uprising that toppled pro-Russian President Viktor Yanukovich, Putin overturned diplomatic convention by declaring Moscow's right to send troops across borders to protect Russian speakers.
In March, Russia seized and annexed Crimea, and in the weeks that followed, armed separatists have taken control of most of the Donbass, which accounts for around 15 percent of Ukraine's population and a third of industrial output.
Moscow has tens of thousands of troops massed on Ukraine's eastern frontier. The outbreak of violence in Odessa, hundreds of kilometres away near a Russian-occupied breakaway region of neighbouring Moldova, means the unrest has spread across the breadth of southern and eastern Ukraine.
Western countries say Russian agents are directing the uprising and Moscow is stoking the violence with a campaign of propaganda, broadcast into Ukraine on Russian state channels, that depicts the government in Kiev as "fascists".
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"Russia sometimes sounds as if it's refighting WW2. Fascism all over the place. Enemies everywhere. Ghosts of history mobilised," tweeted Swedish Foreign Minister Carl Bildt.
However, so far Western concern has not been matched by any serious action that might dissuade Putin. The United States and the European Union have imposed limited sanctions on lists of individual Russians and small firms, but have held back from measures designed to hurt Russia's economy broadly.
Nonetheless, a senior finance ministry official in Moscow said Russian GDP could shrink again this quarter.
NATO has made clear it will not fight to protect Ukraine, instead beefing up defences of its nearby member states. NATO's top military commander, U.S. Air Force General Philip Breedlove, said on Monday Russia had used special forces in eastern Ukraine and he now believed Moscow might be able to achieve its goals without resorting to a conventional invasion.
Western leaders have threatened to impose tougher sanctions on Russia if it interferes with presidential elections in Ukraine set for May 25, and most of their diplomacy has been centred around that date.
"If (the election) doesn't take place, there will be chaos and the risk of civil war," French President Francois Hollande said. "The Russians, Vladimir Putin, at the moment want this election not to happen so as to maintain the pressure. It's up to us to convince them."
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Petro Poroshenko, a Ukrainian confectionery baron who is front-runner in the presidential election, said the vote would go ahead despite the unrest: "We hope that we will be able to complete the anti-terrorist operation before the election. And where we cannot do so - we will surround (those places) and not allow them to interfere with the election."
But Moscow has increasingly dismissed the prospect, suggesting it will not accept the winner of the vote any more than it accepts the interim government in power since February.
"Holding elections at a time when the army is deployed against part of the population is quite unusual," Russian Foreign Minister Sergei Lavrov told a news conference.