Viktor Yanukovych had been declared winner over Yulia Tymoshenko
A Ukrainian court has suspended the result of the recent presidential election, following a challenge by losing candidate Yulia Tymoshenko.
Mrs Tymoshenko, the Prime Minister, made the appeal on Tuesday, claiming the result was rigged. International monitors deemed the vote free and fair.
The court says the result should be suspended while it considers the evidence she has submitted.
The winner, Viktor Yanukovych, is due to be inaugurated on 25 February.
The supreme administrative court ruling concerns the Ukrainian Central Electoral Commission's declaration on Sunday that Mr Yanukovych had won the vote.
The results showed him to have beaten Mrs Tymoshenko by a margin of 3.48%.
The court is due to rule on Mrs Tymoshenko's appeal to have the results thrown out in the coming days.
It says it is not in a position to rule on a separate appeal to have the inauguration of Mr Yanukovych put on hold.
Mrs Tymoshenko has so far rejected Mr Yanukovych's appeals for her to accept defeat.
She has claimed that the election was marred by "systemic, fundamental and general falsifications" and has appealed for a full recount.
She appeared at the supreme administrative court in Kiev on Tuesday with her supporters, carrying several boxes said to contain evidence that the election was fraudulent.
However, international election monitors have said there were no significant flaws in the vote.
Mrs Tymoshenko's challenge is expected to prolong Ukraine's political instability.
The country, which is in the midst of a severe economic crisis, has been in political deadlock for several years.
Mr Yanukovych's election run capped a political comeback from his defeat in the presidential elections of 2004.
After originally being declared the winner in that year, Mr Yanukovych's victory was found to be fraudulent and overturned, following the Orange Revolution led by Mrs Tymoshenko and Viktor Yushchenko.
Mr Yushchenko went on to be president, but was ejected in the first round of this year's vote.
The relationship between Mrs Tymoshenko and Mr Yushchenko later broke down into a poisonous political rivalry.