KIEV, Dec 4: Ukraine's outgoing President Leonid Kuchma on Saturday called European negotiators back to Kiev for a third round of talks to break a new deadlock with the opposition that could throw doubt over a new presidential runoff ordered by the supreme court.

Mr Kuchma charged that agreements reached during previous roundtable discussions "are not being carried out by the opposition, which is leading to an increase of tensions in the country", according to a statement from the presidency.

He made the charge after the pro-Western opposition prevented parliament from adopting constitutional changes that would weaken the presidency and that Mr Kuchma has been trying to push through for several years.

During previous roundtable talks with European negotiators, Mr Kuchma and opposition leader Viktor Yushchenko had agreed to negotiate the passage of the constitutional amendments, along with amendments to the electoral law for a rerun of the invalidated Nov 21 poll, as ordered by the Supreme Court on Friday.

"I am certain that the supreme court's decision is a violation of the Ukrainian constitution and that it was taken under pressure from the street," Prime Minister Yanukovich said in a statement distributed to journalists.

The court has said that its decision is final and cannot be appealed.

The ruling was greeted with deafening cheers by the hundreds of thousands of opposition supporters who have massed in Kiev's central Independence Square round-the-clock for nearly two weeks.

"Yu-shchen-ko! Yu-shchen-ko!" the crowd chanted.

The hero of the hour hailed his supporters shortly after.

"The decision was taken thanks to you, you are heroes," Yushchenko told a veritable sea of supporters clad in the orange colour of his campaign.

"We're going to have awesome fireworks tomorrow," he promised.

The contested vote had split this former Soviet republic of 48 million in half and resonated on the world stage, too, as Russia backed Mr Yanukovich and the United States and the European Union supported Yushchenko's claims.

European heavyweights like Polish President Aleksander Kwasniewski and EU foreign policy chief Javier Solana travelled twice to Kiev to mediate tense negotiations between the opposition and the ruling regime during the nearly two-week standoff.

Washington and Brussels immediately welcomed Friday's court ruling.

"The court's decision is an important step in moving toward a peaceful, democratic resolution that reflects the will of the people," White House spokesman Scott McClellan said.

"I welcome this independent decision ... which opens the way for a repeat of the second round of the election that can fully reflect the will of the Ukrainian people," said EU external relations commissioner Benita Ferrero-Waldner.

As of late Saturday, Russia had yet to issue a comment on the ruling. -AFP