A top Ukrainian official delivered a scathing rebuttal yesterday to criticism from Russia, calling President Dmitry Medvedev a menacing "hostage" to outdated Kremlin imperialist designs.

"Sadly, the young Russian leadership is hostage to an old imperialist complex," said Vira Ulyanchenko, chief of the presidential administration who also holds a top post in President Viktor Yushchenko's Our Ukraine Party.

"That makes it cherish the notion of a foreign enemy and replace a dialogue of equals with the language of insults and threats," Ms Ulyanchenko said in a statement posted on the party's website.

Her statement was published a day after Mr Medvedev, in a letter to Mr Yushchenko released by the Kremlin, accused the Ukrainian leader of "anti-Russian" policy and said Moscow was looking forward to "a new political leadership in Ukraine".

Mr Medvedev's attack marked a sudden and sharp public worsening of the long-prickly relationship between the two giant ex-Soviet republics.

It was also interpreted by some political analysts as an unusual and undiplomatic Kremlin foray into Ukrainian politics much like a premature election congratulations in 2004 that triggered the Orange Revolution.

Ms Ulyanchenko's comments, though released through the party of which both she and Mr Yushchenko are members, however carried considerable state weight, due to her position at the head of Mr Yushchenko's administration.