A coalition of groups loyal to the president and prime minister, collapsed after Yushchenko's Our Ukraine party walked out last week. It denounced Prime Minister Yulia Tymoshenko's tactical voting alliance in the chamber with the more Russia-friendly party of ex-premier Viktor Yanukovich.

"The de facto formation in parliament of a new coalition is the implementation of a political scenario with a sole aim -- to carry out a coup d'etat through a redistribution of powers," the president's press service quoted Yushchenko as saying.

Ukrainian politics has been in turmoil since "Orange Revolution" rallies brought Yushchenko to power in 2004, putting the country at odds with Moscow over the president's drive to move the country closer to the West.

Tymoshenko, his fiery ally during the rallies, was named his first prime minister but was sacked seven months later. She returned to office last year, but the two again quarrelled.

Tymosehnko's bloc and Yanukovich's Regions Party this month approved amendments to legislation reducing the president's powers in favour of the government and parliament.

Yushchenko said he could not understand "a union between a national bourgeoisie and social populists. It is most difficult to say where this 'marriage' might lead."

LOST MAJORITY

Yanukovich draws much of his support from Russian-speaking eastern Ukraine. He was backed by Russia in a 2004 presidential election won by Yushchenko after the Supreme Court ordered a rerun of the ballot on grounds of vote-rigging.

He has since moderated his backing for Moscow, but remains opposed to Yushchenko's key foreign policy plank of securing fast-track membership of NATO.

If the current "orange" coalition, which has anyway lost its majority in parliament, cannot be rebuilt this weekend, parties have 30 days to form a new one. Should they fail, the president can call what would be the third election in as many years.

Yushchenko, in a separate interview with Western newspapers, restated his resolve to win a NATO Membership Action Plan at a December summit of the alliance -- despite limited support among Ukrainians and fierce Russian opposition.

"After events in Georgia, there is only one way to guarantee Ukraine's independence, territorial integrity and sovereignty -- joining collective European security structures," he said.

"It is also in NATO's interests to extend peace and stability eastward."

Russia's Foreign Ministry issued a new warning to Kiev to alter its "unfriendly" stand towards Russia, particularly its "rapid moves to secure NATO membership" and its denunciations of Moscow's intervention in Georgia.