Ukraine votes Sunday in a presidential election aimed at calming a deadly crisis that has threatened the ex-Soviet country's very survival, with a reported cyber attack on the vote-counting system adding to concerns.
A bloody pro-Russia rebellion is set to scuttle voting in the east, a region shaken by the thunder of military tanks and grenade launchers since mid-April.
Prime Minister Arseniy Yatsenyuk issued an appeal for the country's 36 million voters to turn out in force on Sunday to "defend Ukraine" in the most important election since independence in 1991.
"This will be the expression of the will of Ukrainians from the west, east, north and south," he said Saturday.
But the insurgents have threatened to block voting in their strongholds in the rust belt on the Russian border "by force if necessary", ratcheting up the tension in a crisis that has plunged East-West relations to a post-Cold War low.
The West regards the vote as a crucial step in preventing Ukraine from disintegrating further after Russia seized Crimea in March, and has warned Moscow of further sanctions if it disrupts polling.
President Vladimir Putin -- still authorised by parliament to invade Ukraine if necessary to "protect" ethnic Russians -- appeared to make a big concession Friday by saying he was ready to work with the new Kiev team.
"We understand that the people of Ukraine want their country to emerge from this crisis. We will treat their choice with respect," he said.
Russia also says it has started withdrawing from Ukraine's border around 40,000 soldiers and dozens of tank battalions that had been ready to advance at a moment's notice.
The packed field of candidates features clear frontrunner Petro Poroshenko -- a chocolate baron and political veteran who sees Ukraine's future anchored to Europe -- and 17 far less popular hopefuls that include ex-premier Yulia Tymoshenko.
'Somebody broke into the system'
But before voting got under way Ukraine's Interior Minister Arsen Avakov said that the election computer system had been the victim of a cyber attack and that counting would have to be done manually.
"Somebody really broke into the system, erased all data and disrupted the communication with constituency electoral commissions," Avakov said on his personal website.
"This is not a catastrophe. We will count manually. The results will be more accurate," the Interfax-Ukraine news agency quoted the minister as adding.
The election should give the new president and his government a stamp of legitimacy after pro-EU protests forced out Kremlin-backed president Viktor Yanukovych in February, setting off the chain of once-unimaginable events that now threaten the country's unity.
"This election will be decisive for Ukraine," said Kiev's Institute of Global Strategies director Vadym Karasyov.
"This is the first time Ukraine is voting not as a post-Soviet country but an independent one."
However final opinion polls show self-made 48-year-old billionaire Poroshenko falling just short of the 50-percent threshold needed to avoid a second round on June 15, and three weeks of further political uncertainty.
Corruption-stained Orange Revolution co-leader Tymoshenko is battling for the runner-up spot against hawkish former defence minister Anatoliy Grytsenko -- a supporter of Ukraine's membership in NATO -- but is expected to be crushed by Poroshenko in any runoff.
The new president is expected to try to repair relations with Ukraine's former masters in Russia while pushing the nation of 46 million along a westward track.