Ukraine yesterday was plunged into political turmoil as Prime Minister Yulia Tymoshenko refused to acknowledge defeat in presidential elections and her rival called on her to resign.

The election winner, the pro-Russia Viktor Yanukovych, demanded Tymoshenko stand down as Prime Minister, warning that Ukraine did not need a new crisis after being plagued by instability in recent years.

But in the clearest indication yet that Ms Tymoshenko will challenge the results, her top ally said the elections had been marred by extensive violations that cast doubt on the overall outcome.

With political tensions riding high, thousands of Mr Yanukovych supporters yesterday rallied for the third day in a row outside the headquarters of the election commission with the aim of ensuring the results stand.

"I call on the Prime Minister to resign and go into opposition," Mr Yanukovych said in a statement posted on the website of his Regions Party.

"I want to remind Mrs Tymoshenko that the basis of democracy is the will of the people. Democratic leaders always accept the results of the elections.

"The country does not need a new crisis," he added.

Ms Tymoshenko has disappeared from public view since making a short comment on Sunday after the release of exit polls and it was unclear when the usually talkative Prime Minister, famed for her golden hair braid, would reappear.

But Olexander Turchynov, a deputy prime minister and widely seen as Ms Tymoshenko's de-facto number two, emerged to give the highest-level comment from her camp since the results were published.

"In the second round of the Ukrainian presidential elections, falsifications took place which had a substantial impact on the results and put in doubt the outcome of the vote," he said. Mr Turchynov described the violations as "systemic and extensive" and said the Prime Minister's supporters were prepared to challenge the results in the courts.

Mr Yanukovych's campaign manager Mykola Azarov then further raised tensions by describing Ms Tymoshenko as "not a representative of the democratic camp... but rather the camp of totalitarian politicians with fascistic tendencies."

With votes from all polling stations now counted, Mr Yanukovych won 48.95 per cent of the vote, compared to Ms Tymoshenko's 45.47 per ent, the central election commission said, giving him a winning margin of some 3.5 per cent.

Though official, these results are still preliminary and must be formally certified by the election commission, a process which may take some weeks.

Ms Tymoshenko was one of the leaders of the 2004 Orange Revolution that sparked hopes of a new start in the ex-Soviet country bordering the EU and Russia but whose ambitions crumbled amid political infighting and economic crisis.

Mr Yanukovych has long been seen as a pro-Kremlin figure and was accused of staging the vote-rigging in the 2004 presidential elections that sparked the Orange uprising.

In his first major foreign policy statement since the election, Mr Yanukovych issued a clear signal by saying that relations with Russia would be a priority of his presidency.