"The truth is, we have an act of international terrorism on our hands. I happen to believe I know who is behind the death of my friend Sasha (Litvinenko) and the reason for his murder," Yuri Shvets said in an exclusive interview with the AP by telephone from the United States.
Shvets, also a former KGB officer, said he had known ex-Soviet spy Alexander Litvinenko, who died in London after he was exposed to a rare radioactive element, since 2002 and had spoken to him on Nov. 23, the day he died.
He said he was questioned by Scotland Yard officers and an FBI agent in Washington last week. A police official in London, speaking on condition of anonymity because of the sensitive nature of the case, confirmed officers had interviewed Shvets.
The official also said police were "poised" to leave London for Russia and expected to fly to Moscow within days.
Home Secretary John Reid said Sunday the inquiry was expanding and would go wherever "the police take it."
"Over the next few days I think all of these things will widen out a little from the circle just being here in Britain," Reid told Britain's Sky News television.
Reid planned to discuss the death at a meeting of European interior ministers in Brussels on Monday.
Toxicologists found polonium-210, a rare radioactive substance, in Litvinenko's body before he died in London. Results of a post mortem examination on the 43-year-old's body are expected later this week.
Shvets told the AP he also knew Mario Scaramella, an Italian security consultant who met Litvinenko at a central London sushi bar on Nov. 1 — the day he fell ill.
Scaramella was undergoing hospital tests Sunday after he showed signs of the same radioactive substance. University College Hospital said in a statement he was well and showing no external symptoms.
Doctors previously said Scaramella had been exposed to a much lower level of polonium-210 than Litvinenko.
Shvets declined to confirm the name of the person he told police he believed was behind Litvinenko's death, or to offer details of a document he said he had given to the British officers.
"This is first-hand information, this is not gossip. I gave them the first-hand information that I have," Shvets told the AP.
He said he was not prepared to disclose futher details, because of concern he could disrupt the inquiry.
"I want this inquiry to get to the bottom of it, otherwise they will be killing people all over the world — in London, in Washington and in other places," Shvets said. "I want to give the police the time and space to crack this case, to allow them to find those behind this assassination, the last thing I want to do is give a warning to those who are responsible."
Shvets told the AP he had met Litvinenko in 2002, when both men were investigating incidents in the Ukraine. He said he had met Scaramella in the U.S. at Litvinenko's insistence.
The former agent has spoken about his past as a KGB spy during work at the Center for Counterintelligence and Security Studies, in Washington.
Shvets, who also lives in Washington, said he was currently away from his home and somewhere in the U.S. on vacation, but would not confirm his precise location because of concern for his personal security.
"I want to survive until the time we have a criminal case in relation to Sasha's death brought before a court in London," Shvets told the AP.
In a separate statement issued through Tom Mangold, a London-based former British Broadcasting Corp. reporter and his friend of 15 years, Shvets denied claims published Sunday in Britain's Observer newspaper that he had been involved in the drafting of a dossier on Russian oil company Yukos.
Former Yukos shareholder Leonid Nevzlin, a Russian exile living in Israel, told the AP last week that Litvinenko had given him a document related to Yukos and said he believed the agent's killing was tied to his investigations into the company.
Mangold said Shvets had denied the newspaper report, which said he had examined charges filed by Russian prosecutors against Yukos officials and shareholders, handing his findings to Litvinenko.