The Ukrainian opposition has taken its case to the Supreme Court as foreign leaders are asked to help resolve the bitter presidential election dispute.
Yushchenko has urged his supporters to keep protesting
Liberal opposition leader Viktor Yushchenko called for a general strike after election officials declared Prime Minister Viktor Yanukovych the winner.
Yanukovych supporters have vowed to ignore the strike call while opposition protests continue in the capital, Kiev.
A deputy minister has resigned in protest at the controversial poll.
"When the European community does not recognise the results of the election, what kind of European integration we can speak of?" said Oleg Hayduk, Deputy Minister for Economics, as he announced his departure.
President Vladimir Putin of Russia, visiting The Hague for a summit with European Union leaders, called for the dispute to be settled in the courts and urged restraint.
"We have no moral right to push a major European country to mass mayhem," he told EU leaders who said they could not recognise an election result which failed to meet international standards.
According to the official election result, Mr Yanukovych won with 49.46% of the vote against Mr Yushchenko's 46.61%.
Mr Yushchenko's supporters say the authorities oversaw massive fraud in Sunday's election - and independent observers have also reported widespread abuses.
An official at Mr Yushchenko's headquarters confirmed that a complaint had been filed at the Supreme Court over the handling of the poll by the Central Electoral Commission (CEC).
Correspondents say the court is seen as a comparatively independent body.
Since the strike call, reports speak of major traffic jams on Ukraine's western border where several main roads have been blocked, and some factories and universities are said to have stopped work.
However, coalminers in the east of the country, where Mr Yanukovych's strength lies, have vowed to work on and the Yushchenko camp has been condemned as "traitors".
Some analysts say the strike could further divide the country as Mr Yushchenko draws his support mainly from western and central regions.
Leonid Kuchma, the outgoing Ukrainian president and ally of Mr Yanukovych, has asked Polish President Aleksander Kwasniewski and Lithuanian President Valdas Adamkus to mediate in the crisis.
Yanukovych (left): 49.46%
Western observers report:
Abuse of state resources and "overt media bias" in favour of Mr Yanukovych
State workers pressured to give absentee voting certificate to their superiors
Intimidation at some polling stations
Suspiciously high turnout - 96% - in the key pro-government region of Donetsk
Mr Kwasniewski, said to have close ties with Mr Kuchma, confirmed that he would visit Ukraine "in the next few days".
Lech Walesa, a former Polish president and ally of Mr Yushchenko, has already gone to Kiev to try to help to resolve the crisis, saying he believes a compromise is possible.
Mr Kuchma has warned that civil war "could well become a reality".
Government supporters have begun holding rallies in Kiev but the capital is still dominated by thousands who back Mr Yushchenko. They have been camping out in the main square in freezing temperatures under orange banners.
"The orange revolution is on the march," Mikola, a 21-year-old student, told AFP news agency in Independence Square on Thursday.
"The days of the bandits in the presidency are numbered!"
A 40-year-old woman passer-by, Svetlana, said that for the first time in her life, she was "proud to be Ukrainian".