The investigation into the poisoning of Alexander V. Litvinenko, a former Russian K.G.B. operative, will likely broaden in coming days, Britain’s highest ranking law enforcement officer said today, and news reports said British counterterrorism officers were planning to fly to Moscow to interview witnesses.

The investigation into the poisoning of Alexander V. Litvinenko, a former Russian K.G.B. operative, will likely broaden in coming days, Britain’s highest ranking law enforcement officer said today, and news reports said British counterterrorism officers were planning to fly to Moscow to interview witnesses. 2

The investigation into the poisoning of Alexander V. Litvinenko, a former Russian K.G.B. operative, will likely broaden in coming days, Britain’s highest ranking law enforcement officer said today, and news reports said British counterterrorism officers were planning to fly to Moscow to interview witnesses.

Mr. Litvinenko died Nov. 23 of radiation poisoning, and a radioactive isotope, polonium 210, was found in his urine. Since then, the investigation into his death has led the police along a trail of places where traces of radiation were found — including British Airways airplanes flying to and from Moscow and several locations in central and north London.

The reported plan to send officers to Moscow has deepened speculation that the British police are looking increasingly to Moscow for information about the origins of the poison and the identity of people who may have been in contact with Mr. Litvinenko before his death. Mr. Litvinenko had, since the late 1990s, become a staunch critic of President Vladimir V. Putin of Russia.

The possible Russian connection has already spilled into the realms of diplomacy. Senior Russian officials have complained to their British counterparts about the publication of a death-bed testament by Mr. Litvinenko accusing Mr. Putin of responsibility for the poisoning, according to a British official who spoke in return for anonymity under civil service rules. Still, Moscow has said it will cooperate in the British investigation.

Shortly before his death, Mr. Litvinenko secured British citizenship, according to his associates, and that has raised the diplomatic stakes, particularly if foreign agents were responsible for his death, which would make it an assassination on British soil.