LONDON -- Britain's senior law enforcement official said Sunday an inquiry into the death of a former KGB agent had expanded overseas, and a U.S.-based friend of the former agent said he told police the name of the person he believes orchestrated the poisoning.

Yuri Shvets said had known the poisoned ex-spy, Alexander Litvinenko, since 2002 and spoke with him on Nov. 23, the day Litvinenko died following his exposure to a rare radioactive element, polonium-210.

"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 and the reason for his murder," Shvets said in an exclusive interview with The Associated Press by telephone from the United States, referring to Litvinenko by his Russian nickname.

Shvets, also a former KGB officer, declined to confirm the name of the person he believed was behind Litvinenko's death because of concern it could disrupt the investigation. He also declined to offer details on a document he said he had given to the British officers.

"This is firsthand information, this is not gossip. I gave them the firsthand information that I have," Shvets told the AP.

Shvets 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.

Home Secretary John Reid said Sunday the inquiry would go wherever "the police take it."

"Over the next few days I think all of these things I think will widen out a little from the circle just being here in Britain," Reid told Britain's Sky News television.

The British police official said police were expected to travel to Russia in coming days to interview a number of people, including Andrei Lugovoi. Lugovoi is another former Russian spy who met with Litvinenko on Nov. 1, the day Litvinenko fell ill.

The Sunday Times newspaper quoted Lugovoi as saying he had also been contaminated with polonium-210, but he did not say whether he had fallen ill. He denied that he and two business associates who accompanied him to the Nov. 1 meeting were involved in Litvinenko's death.

"We suspect that someone has been trying to frame us," the Times quoted Lugovoi as saying. "Someone passed this stuff onto us ... to point the finger at us and distract the police."

Repeated attempts by the AP to reach Lugovoi in Moscow through a business associate have been unsuccessful.