By Richard Balmforth and Pavel Polityuk
KIEV (Reuters) - Ukraine's re-energized opposition on Monday threatened President Viktor Yanukovich with impeachment and vowed to work to free ex-prime minister Yulia Tymoshenko from jail as they set out an action program for the new parliament.
The three parties, which include Tymoshenko's Batkivshchyna (Fatherland), far-right nationalists and a liberal party headed by boxing champion Vitaly Klitschko, made their call in a joint statement in which they grudgingly accepted the results of the disputed October 28 election.
The opposition's bold move, in which they swore to defeat "the regime of Yanukovich", raised the political temperature on the eve of a possible resumption on Tuesday of a second trial of Tymoshenko in the eastern city of Kharkiv.
But final election figures show that Yanukovich's Party of the Regions seems set to hang on to a majority in the 450-seat parliament - with the help of traditional allies - and it should be able to hold the opposition at bay in the new parliament.
The election in the former Soviet republic, mid-way through Yanukovich's five-year presidential term, has been criticized as flawed by international observers.
Despite the international criticism and street protests by the opposition, the election's outcome is likely to be used by Yanukovich as a springboard from which to launch a second bid for presidential office in 2015.
The three opposition parties, which made a strong showing and secured 178 parliament seats despite the absence of Tymoshenko, now appear to have agreed to take up their place in parliament even though they are still contesting voting in a few electoral districts.
Yanukovich's pro-business Regions, which is financed by wealthy industrialists, says it alone can provide stability in Ukraine, a major exporter of steel and grain.
The three opposition parties, which include the Svoboda (Freedom) Ukrainian nationalist party and Klitschko's UDAR (Punch), say his rule will extend corruption and cronyism, and relations with the West will deteriorate further.
The European Union has frozen a free trade agreement with Ukraine over the Tymoshenko affair.
In their statement, the opposition parties vowed to work for a law under which Yanukovich could be impeached - something which has been actively blocked by Regions deputies in parliament - and for the resignation of the Yanukovich government and police and justice chiefs.
Opposition parties - particularly Batkivshchyna and Svoboda - reproach Yanukovich for signing an agreement with Russia in April 2010, shortly after he came to power, which extended the base rights of Russia's Black Sea fleet in Ukraine's Crimea until 2042.
"The resignation of the President, the government and the state prosecutor: these are our three main political tasks," Arseny Yatsenyuk, who heads Batkivshchyna in the absence of Tymoshenko, told a crowd of about 1,000 opposition supporters on Monday night.
"The very fact that three political forces have agreed to a joint start means that the opposition train has set off towards a new, honest, European country," Svoboda leader Oleh Tyahnibog declared to the same crowd in front of the Kiev headquarters of the central electoral commission.
The opposition also pledged to secure the freedom of Tymoshenko, 51, who was jailed in October 2011 for abuse of office after a trial which she said was a vendetta by Yanukovich, who beat her narrowly for the presidency in February 2010. The West has denounced her case as 'selective justice'.
Tymoshenko, a leading light in the "Orange Revolution" protests of 2004-5 which doomed Yanukovich's first bid for the presidency, is now on hunger strike in Kharkiv in protest at what she says was gross electoral fraud by the Regions.
A second trial on equally serious charges of embezzlement and tax evasion is due to resume against her on Tuesday, though there is a strong possibility the hearing may be postponed.
Her supporters called on her to end her hunger strike.
"We ask you Yulia: don't continue your hunger strike ! We need you strong, alive and healthy," declared Yatsenyuk to the crowd on Monday.
Despite the appearance of unity, the three opposition leaders have differences among themselves which could yet doom their partnership. Svoboda's Tyahnibog and UDAR's Klitschko are particularly known to be on poor terms with each other.
(Writing By Richard Balmforth; Editing by Andrew Heavens)