Ukrainian President Viktor Yushchenko has urged Russia to turn over important figures in his nearly lethal dioxin poisoning five years ago.

Yushchenko said in an interview aired Sunday night on Channel 1+1 that the testimony of the three men who were at a dinner in 2004 at which he believes he was poisoned is crucial to finishing the investigation.

"These three people who directly received me, treated me and served me, today unfortunately are in Russia," Yushchenko said.

He said the extradition make it possible to determine "who poisoned the president, what the motives were and who must be held responsible for this."

Ukrainian prosecutors said last year that they had failed to identify a suspect. Prosecutors declined comment on Yushchenko's statement Monday and refused to say whether any suspects have now been named.

Ukrainian prosecutors said Russia has refused to extradite one of the men, the former deputy chief of Ukraine's security service, Volodymyr Satsyuk, because he holds both Russian and Ukrainian citizenship.

Russian prosecutors also declined comment.

Yushchenko fell gravely ill while competing against a Russia-backed rival in the 2004 presidential campaign. He was later diagnosed with dioxin poisoning, which badly scarred his face. He won the election on a wave of massive public protests dubbed the "Orange Revolution."

Yushchenko has continuously accused Moscow of stalling the investigation by refusing to extradite important figures in the case or to provide Russian-made dioxin for testing. He has said repeatedly that he knows who was responsible for the poisoning but does not want to name anyone while an investigation continued.