President Yushchenko of Ukraine accused his prime minister of committing “high treason” by not speaking out against the Kremlin during an escalating stand off with Russia.

The feud between the one-time allies over Ukraine’s strategic outlook raised fears that Kiev is vulnerable to political chaos should Moscow hatch a campaign to destabilise a second pro-Western neighbor having humiliated Georgia.

Aides to Mr. Yushchenko, who has incurred Russia’s wrath by taking measures to retaliate against Moscow’s aggression in Georgia, said Prime Minister Tymoshenko was plotting to use a deepening crisis with Moscow to take over as president.

“The actions of the current prime minister show signs of high treason and political corruption,” the president’s deputy chief of staff, Andriy Kyslynskyi, said. “We said last week that Tymoshenko systematically works in the interests of the Russian side. Unfortunately, this information is being confirmed.”

Mr. Kyslynskyi hinted that Mr. Yushchenko would seek a secret service investigation of the alleged acts of national betrayal committed by Ms. Tymoshenko. A spokesman for Ms. Tymoshenko refused to comment on the allegations.

Although the presidential official provided no evidence to back up the assertion that crimes had been exposed, the remarks took a developing confrontation between the two liberal reformers to a new level.