By Richard Balmforth
KIEV (Reuters) - Lawmakers loyal to Ukrainian President Viktor Yanukovich caused political uproar on Thursday when they stormed out of parliament where the opposition was blocking proceedings and set up a rival assembly in a nearby building.
The deputies from the ruling Party of the Regions, which with communist allies holds a majority, moved into their new premises and began voting on laws in a move denounced by one opposition leader as a Soviet-style coup d'etat.
The tactic plunged Ukraine into fresh turmoil that was certain to rebound on its already damaged image with Western institutions and governments.
The Kiev government is negotiating with the International Monetary Fund for a new $15 billion bail-out and also seeking to convince a skeptical European Union that it is a fit partner to sign a free trade agreement this year despite the jailing of opposition leader Yulia Tymoshenko.
Opposition lawmakers, led by heavyweight boxer Vitaly Klitschko, former economy minister Arseniy Yatsenyuk and far-right nationalist Oleh Tyahnybok, have regularly blocked parliamentary proceedings by surrounding the speaker's rostrum in a show of force after gaining strength in an October election.
They resorted to the same tactic after losing a vote on Tuesday to secure an election in June for Kiev city mayor. This means a Yanukovich appointee could stay in control of the capital until after Yanukovich makes a bid for a second presidential term in 2015.
As Regions deputies quit the 450-seat chamber and decamped to another building about 500 meters away, Regions faction leader Olexander Yefremov defended their action as legitimate and in line with the Constitution.
"Parliament can with 226 votes take a decision about holding a session in a separate place and this will be quite within the law," Yefremov said.
But the action drew sneers from the opposition. Yatsenyuk, speaking in the chamber of the traditional parliament building, denounced it as a Soviet-style putsch like that of communist hardliners against Soviet leader Mikhail Gorbachev in 1991.
"After today's illegal attempts to seize power, Ukraine will definitely rise up," he said.
"The way the so-called majority has run away from the walls of the parliament testifies to the inability of the Yanukovich regime to direct its policy," said Tyahnybok.
The fresh bout of turmoil comes while the Kiev government is hosting a visit by an IMF mission from which it hopes to secure fresh loans of $15 billion to help it service foreign debts of around $9 billion falling due this year.
Analysts say the parliamentary disarray is only likely to tell against the former Soviet republic in talks with the EU. The 27-member bloc has already suggested that backsliding on democracy could cost Kiev the signing of key agreements on political association and free trade at the end of the year.
The EU warned Yanukovich in February that the trade deal could be jeopardized if Ukraine did not show progress towards political reform by May.
For the EU, the deal is conditional on improved human rights and ending the practice of "selective justice" - meaning the jailing of political opponents such as former prime minister Tymoshenko, Yanukovich's arch rival who is serving a seven-year jail sentence for abuse of office.
(Reporting by Olzhas Auyezov and Pavel Polityuk; Editing by Andrew Heavens)