Spy chief Valentyn Nalyvaychenko said the Russians had been caught in the Odessa region trying to obtain military secrets.

"Ukraine's security services intercepted a Russian intelligence operation on Jan. 27 in the region of Odessa," Nalyvaychenko said, Interfax reported.

"We caught all five operatives red-handed who, with blackmail and threats, tried illegally to obtain Ukrainian state secrets from a Ukrainian citizen," he said in comments confirmed by a spokeswoman for the security service.

Nalyvaychenko said the spy group — which included officers from the Federal Security Service and a Russian soldier stationed in Moldova's breakaway region of Transdnestr — had kidnapped a Ukrainian in an attempt to gain secrets.

He said four of the Russians had been expelled from Ukraine and an FSB colonel had been arrested on espionage charges.

Digital recorders, a video camera disguised as a fountain pen, flash cards, notebooks, instructions and $2,000 intended to bribe the Ukrainian were found, he said.

A Moscow-based spokesman for the FSB declined to comment.

The spy scandal has broken between rounds of a tense election for president in Ukraine in which relations with Russia is an issue.

It came hot on the heels of the arrival of Russia's new ambassador to Kiev, Mikhail Zurabov, ending a five-month diplomatic rift.

Relations with Moscow had deteriorated under President Viktor Yushchenko, but he failed to gain re-election in a first round of voting, prompting Moscow to finalize Zurabov's appointment, which had been delayed.