Ukraine's parliament on Tuesday fixed February 25 for the inauguration of Viktor Yanukovich as president, even as rival Yulia Tymoshenko prepared to challenge his election in court.

A majority of 238 deputies in the 450-seat chamber voted in favor of the date for Yanukovich's swearing-in which follows a February 7 runoff vote against Tymoshenko, the prime minister, who says the poll was fraudulently conducted.

Supporters of Tymoshenko, who lost the vote by a narrow margin of 3.5 percentage points according to official results, were due on Tuesday to begin their appeal in a Kiev high court.

She says that cheating by the Yanukovich camp -- which is denied by him -- robbed her of victory and she says she does not recognize him as a legitimately elected president.

A member of the Our Ukraine party faction, which is allied to the Tymoshenko bloc, said that in talks between the factions on Tuesday Tymoshenko had repeated that she would not step down voluntarily as prime minister.

Although she is unlikely to succeed in her legal challenge to the result, the move will prolong uncertainty in the former Soviet state of 46 million, which has been hit by economic crisis and is making do without a $16.4 billion IMF program, suspended last year.

(Writing by Richard Balmforth and Sabina Zawadzki; Editing by Louise Ireland)