By Yuri Kulikov and Sabina Zawadzki
KIEV (Reuters) - Ukrainians voted on Sunday in a bitterly contested presidential run-off between Prime Minister Yulia Tymoshenko and opposition leader Viktor Yanukovich which threatened to sow further instability in the ex-Soviet republic.
Analysts expect a narrow victory for Yanukovich, an ex-mechanic. But former gas tycoon Tymoshenko has threatened to replay the "Orange Revolution" that denied Yanukovich the presidency after a rigged vote in 2004.
Complaints by Tymoshenko's camp of "banditry and terrorism" before the polls closed suggested a challenge to the result was likely if she loses.
A disputed result would further damage confidence in a country plagued by years of political bickering between "Orange" revolutionaries Tymoshenko and President Viktor Yushchenko, stalled policy-making and more recently an economic crisis.
"Orange" euphoria has given way to frustration and fatigue.
"It would be terrible to vote for Tymoshenko. It would be shameful to vote for Yanukovich," 27-year-old Natalya Zhuk said in the snow-bound capital, Kiev. "Nothing in this country will change in the next five years."
Before polls were due to close at 8 p.m. (6 p.m. British time), Tymoshenko's camp said it would contest results in around 1,000 polling stations in the eastern Donetsk region, the industrial power base of Yanukovich.
Deputy Prime Minister Oleksander Turchynov, Tymoshenko's campaign chief, complained of multiple-voting and bribery.
Turchynov said a local election official from Tymoshenko's party in the western Ivano-Frankivsk region had died from head injuries while defending a safe containing ballot papers. But the central election commission said the man had died from a heart attack, and Russia's RIA news agency quoted a local police chief as confirming this, adding: "He died outside the polling station."
Both Tymoshenko, 49, and Yanukovich, 59, hope to improve ties with Russia after relations with the ex-Soviet master deteriorated under outgoing president Yushchenko.
Both also hope for closer integration with the European Union, though Tymoshenko is seen as more enthusiastic. Yanukovich was tagged Moscow's stooge in the revolution.
Whoever wins must make difficult spending cuts at home to bring back the International Monetary Fund and its $16.4 billion (10.5 billion pounds) bailout for Ukraine that was vital for the state coffers but suspended last year over broken promises.
"I am sure that the Ukrainian nation deserves a better life," a smiling Yanukovich said casting his ballot. "That is why I have voted for good changes, for stability and for a strong Ukraine."
He led Tymoshenko by 10 percentage points in the first round on January 17. By 3 p.m. (1 p.m. British time), 50.5 percent of those eligible had voted, lower than in previous elections but slightly higher than in the first round.
Reflecting the unhappiness of many, a group of semi-naked women overran the polling station where Yanukovich was due to vote with placards saying "Stop raping the country," asking people not to "sell" their votes.
Antagonism between the beefy, slow-speaking Yanukovich, 59, and the sharp-tongued Tymoshenko, 49, mirrors a gulf between the Russian-speaking east and nationalist west in the country of 46 million people.
In the east and south, people have faith in Yanukovich's consistency and his ability to do business with Russia, seeing him as a strong man shaped by a rough childhood. He has served twice as prime minister -- the same as Tymoshenko.
"We lost five years of our lives thanks to Yushchenko and Tymoshenko," said Oleg Nochvyn, a miner in his 50s.
"For five years they were promising us -- tomorrow will be better. Well, I get up the next day and it's worse than the day before ... Under Viktor Fyodorovich (Yanukovich) we had everything -- economic growth, everything was getting better."
A tired Tymoshenko voted early in her native Dnipropetrovsk.
"I have just voted for a new Ukraine, a happy Ukraine, a rich, beautiful European state," she said. "I am sure only in such a state people will live happily, each person will find his place and I will serve this cause with all my soul and ability."
Yushchenko, Tymoshenko's former ally in the Orange Revolution but with whom she has since exchanged bitter recriminations, was eliminated in the first round of voting.
"I think Ukraine will be ashamed of its choice. But that is also democracy," Yushchenko said.