KIEV (AFP) - Ukrainians voted Sunday in their third national poll in three years, aimed at ending months of political unrest with pro-Western parties seeking to push their Russian-backed rival from power.

The election for the parliament, the Rada, was called to resolve a feud between Western-leaning President Viktor Yushchenko and his prime minister, Viktor Yanukovych, who is closer to Ukraine's former ruler Moscow.

The contest was expected to be extremely tight, with no party likely to gain an outright majority and no end in sight to the turmoil gripping Ukraine since the 2004 pro-democracy "Orange Revolution."

Yanukovych's Regions Party was forecast to win the most votes.

But Yushchenko hopes an alliance with Yulia Tymoshenko, his partner in the "Orange Revolution," will enable him to form a coalition government and oust Yanukovych.

"I am convinced that today the nation will choose change," Yushchenko said after voting with his wife and daughter on a balmy autumn day in central Kiev.

The president sought to calm fears that months of street protests and constitutional paralysis would continue in the ex-Soviet republic of 47 million people.

"The political community will reach agreement," he vowed.

Tymoshenko, who is vying to become the next prime minister, also promised not to waste time in setting up a new government.

"Voters are tired of waiting," she said as she voted in the eastern town of Dnipropetrovsk.

But Yanukovych, who aims to retain his hold on the premiership, said Ukraine was "being put to the test," and warned he would not recognise the results in the case of "total lawlessness" in the poll.

Washington, the European Union and an increasingly assertive Kremlin are closely watching this strategically placed country, which has expressed interest in joining both the European Union and NATO.

Sandwiched between Russia and the European Union, Ukraine straddles key Russian gas export routes to energy-hungry EU clients.

It is also a testing ground for Western-style economic and political reforms in the former Soviet Union, where many countries are now headed by authoritarian governments.

The tightness of the race, in which 20 parties were taking part, meant coalition talks were inevitable, with no end in sight to deep divisions between the Russian-speaking east and Ukrainian-speaking west of the country.

Yushchenko's Our Ukraine-People's Self Defence party and the Yulia Tymoshenko Bloc hope to win enough combined votes to form a new government, with Tymoshenko replacing Yanukovych as premier.

However, polls predict Yanukovych's Regions Party will come a close second to the combined "Orange" parties. The prime minister may still be able to form a majority coalition if any of the 17 smaller parties manage to win seats.

Although some Ukrainians are fed up with the endless political wrangling, passions remain high in what is arguably the most vibrant democracy of the Russian-dominated ex-Soviet bloc.

Oleg Petrovich, a 55-year-old engineer, said he backed the Regions Party as the only alternative to "the idiotic 'Orange' people."

"At least Regions Party have brought some kind of stability. There's been work for people since they came," he said after voting in Kiev. "We should join with Russia, then everything would be alright."

But in the western Ukrainian city of Lviv, Hrigory Lutsiv, 34, said he had voted for Tymoshenko "in order to support our entry into NATO and the EU, and to put Yanukovych and his gang in prison -- and for Yulia to become premier."

At least 50 percent of the 37 million registered voters must take part for the election to be valid. Turnout reached 20 percent after five hours of voting, the Central Electoral Commission said.

In the 2004 "Orange Revolution," huge popular protests forced Yanukovych to agree to a rerun of a flawed presidential election in which he had defeated Yushchenko.

Yanukovych was beaten in the rerun, but returned as premier after his party won a parliamentary majority in March 2006 elections.

The upheaval of the "Orange Revolution" sent shockwaves through Russia's political establishment, which had closely backed Yanukovych.

There were fears that Sunday's election would be marred by cheating, prompting a new round of turmoil.

Polls opened at 7:00 am (0400 GMT) and were due to close at 10:00 pm (1900 GMT).

In an incident apparently unrelated to the election, a policewoman shot herself in a polling station in the eastern town of Mariupol. Police said the woman had committed suicide, using her service pistol.