Former deputy head of the Ukrainian secret police Volodymyr Satsyuk has been questioned over his involvement in the 2004 dioxin poisoning of former President Viktor Yushchenko, Ukraine`s prosecutor general Viktor Pshonka said, according to RIA Novosti.

"Satsyuk was officially questioned by the investigators of the Russian Prosecutor General`s Office in the presence of our representatives and upon our request," Pshonka said in an interview with the Segodnya newspaper.

Satsyuk gave some "very important" details to the investigation, which had previously been unknown, Pshonka said.

Yushchenko fell ill shortly after discussing the 2004 presidential election campaign over dinner at Satsyuk`s residence.

The next day, Ukrainian doctors diagnosed food poisoning, and four days later, as his condition failed to improve, Yushchenko was taken to the Rudolfinerhaus clinic in Vienna, which he left later in the month for the election campaign.

Medical experts from the United States, Austria and UK investigating his illness were divided over the cause, but in late 2004 the Rudolfinerhaus clinic confirmed that he had been poisoned with dioxin.

Yushchenko accused Russia, which supported his opponent in the election race, of being behind the poisoning. Satsyuk, who denied any involvement in the poisoning, was given Russian citizenship and is currently living in Moscow.

In the interview, the Ukrainian prosecutor general said the theory that Yushchenko was not poisoned at all had not been ruled out. "But if there was no poisoning, we need conclusive evidence of this," he said.