The warning came after Ukraine's pro-Russia regions threatened to split from the European-leaning west of the country amid the crisis that has left Moscow and Western capitals glowering at each other across a Cold War-like divide.

"The unity of Ukraine is fundamental," said EU foreign policy chief Javier Solana, who travelled to Ukraine last week to try to mediate in the crisis following contested presidential elections.

"Any kind of threats of that nature are not very welcome," he added.

North Atlantic Treaty Organization (NATO) chief Jaap de Hoop Scheffer meanwhile underlined "the importance of territorial integrity of Ukraine."

"The sense of belonging to one nation is very important here ... on that basis a solution should be found," he said.

The remarks came as Ukraine's top court convened to try to resolve the week-long crisis pitting pro-Russian Prime Minister Viktor Yanukovich against pro-West opposition leader Viktor Yushchenko.

The supreme court was considering opposition claims that massive fraud helped Yanukovich win the November 21 election. Yushchenko insists that he was robbed of victory and is demanding a re-run of the poll on December 12.

Solana said he hoped the Kiev court ruling would help. "Today is a very important day. ... Let's hope the response of the supreme court will help," he said.

Ukraine's Yanukovich bastions in the southeast have warned that they would declare greater autonomy if their candidate fails to become president, fanning fears that the crisis could split the former Soviet republic.

Asked about the threat of secession, Solana said: "It is fundamental that dialogue and politics be continued.

"What we have to avoid at all means possible is the outbreak of violence. ... This is a difficult problem but it has to be resolved by politics and not by any other means," Solana added.

European Commission spokeswoman Francoise Le Bail reiterated the warning against a division of Ukraine.

"It is very important for us that a schism in Ukraine is avoided," she said.

"What is important for us is that the parties concerned in Ukraine can find a way out of this crisis in an independent way and find a way which will sort out the problem so that the will of the Ukrainian population is respected."

The spat is increasingly reminiscent of a Cold War-era dispute between East and West.

The US and European capitals say they are simply standing up for democracy in a neighbor. But Moscow has angrily accused the West of fomenting unrest to wrest Ukraine from Russia into its sphere of influence.

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