Ukraine was on Saturday completing its last day of preparations for the run-off presidential election, with officials predicting a legal battle after the voting no matter the result, dpa reported.
"I am 99 per cent sure, the election's result will ultimately be decided in the courts," said Andry Mager, vice national election committee chairman, via a web-transmitted press conference. "For sure there will be a law suit."
Prime Minister Yulia Tymoshenko, a populist politician running on an anti-corruption ticket, faces former Prime Minister Viktor Yanukovych, a politician closely linked with big business, in the Sunday run-off.
A law banning election campaigning on the day before the actual vote was in effect on Saturday, with no major violations reported.
Both Yanukovych and Tymoshenko made public appearances in the capital Kiev on Friday evening, and statements on national news programmes, in the last hours before the ban went into effect.
Yanukovych at a rally attended by some 2,000 supporters repeated campaign promises to give the Russian language equal status with Ukrainian for use in courts, education and business - and to improve relations with Ukraine's giant northern neighbour Russia.
Tymoshenko - dressed in her trademark white - to attend a service and confess at Ukraine's oldest St Sofia cathedral, and later told reporters she "apologised for the failures" of her government.
Yanukovych is likely to defeat Tymoshenko by between an 8 and 11 per cent margin, according to the most recent election polls.
Tymoshenko and Yanukovych in recent weeks have traded accusations of possible election fraud to skew Sunday's voting results.
More than 3,500 international monitors were on hand in Ukraine on January 17, during the first round of Ukraine's presidential vote.
The poll was fair and without major violations, officials from the Organization for Security and Cooperation in Europe (OSCE) later said.