Western observers, including the United States on Tuesday called the win of Ukraine's ruling party in the country's elections a "step backwards" for the ex-Soviet nation and further isolating the increasingly controversial President Viktor Yanukovych.

Yanukovych's Regions Party was set to win the polls against Tymoshenko's opposition bloc and the UDAR (Punch) group of boxer Vitali Klitschko, with some predicting it would have a thin overall majority in the new parliament.

Results based on 90.6 percent of the precincts reporting showed the Regions Party collecting 31.4 percent of the ballot and Tymoshenko's alliance registering 24.6 percent.

The Communist Party and UDAR were almost tied on 13.7 and 13.5 percent of the vote respectively, while the nationalist Svoboda (Freedom) group, loosely allied with Tymoshenko, would also make it into the chamber with 9.8 percent.

But the opposition pointed to independent exit polls that had showed Tymoshenko's bloc only trailing the Regions Party by about four percentage points.

"These elections were falsified from start to finish," Tymoshenko said in a statement read by her lawyer Sergiy Vlasenko late on Monday.

The fiery 2004 Orange Revolution leader and former premier – sentenced to seven years on abuse of power charges she views as the president's personal vendetta – said she would go on hunger strike "until the true results are established".

The final composition of the 450-seat Verkhovna Rada will be determined half by the proportional vote and half by first-past-the-post results in single mandate constituencies where the Regions Party has polled especially well.

In the single mandate count, the Regions Party was set to win seats for 117 constituencies, the Tymoshenko bloc 43 seats, Svoboda 10 and UDAR five.

The other seats are set to go to marginal parties and independents, many of whom analysts believe will turn out to be loyal to the Regions Party and give it an overall majority in the new parliament.

"We expect these results to hold," Prime Minister Mykola Azarov told reporters. "This means that the Regions Party has scored a resounding victory."

Reversal of progress

Observers from the Organisation for Security and Cooperation in Europe (OSCE) piled pressure on Yanukovych by calling the elections a reversal of Ukraine's democratic progress.

"Considering the abuse of power, and the excessive role of money in this election, democratic progress appears to have reversed in Ukraine," said OSCE special coordinator Walburga Habsburg Douglas.

Douglas also pointed out that Western officials had to go to various jails to hear leading opposition voices because both Tymoshenko and allies such as ex-interior minister Yuriy Lutsenko had all been convicted of abuse of power.

OSCE representatives Tuesday wanted to visit Tymoshenko – currently hospitalised with back pain in the eastern city of Kharkiv – but the prisons service said this was impossible as doctors were supervising her due to the hunger strike.

Both Washington and Brussels came down heavily on Ukraine after the elections in statements that drew only a cautious response from the Ukrainian foreign ministry.

Acting US State Department spokesman Mark Toner backed the OSCE's description of the poll as "a step backwards" for democracy, saying Washington was "troubled by allegations of fraud and falsification in the voting process."

The European Union also put Ukraine on notice that it would be watching it carefully after a vote foreign policy chief Catherine Ashton and EU commissioner for enlargement Stefan Fule described as a "mixed picture with several shortcomings".

The Ukrainian foreign ministry issued a statement Monday promising to "carefully analyse" the observers' criticisms and "improve the election legislation and practice".