Leonid B. Nevzlin

MOSCOW — Russia's Prosecutor General's Office on Wednesday produced a startling new twist in the investigation of the killing of Alexander V. Litvinenko, the former KGB officer who died in London in November of radiation poisoning.

It announced that it was investigating the possible involvement of former executives of Yukos Oil, the company dismantled by a prosecutorial assault last year.

In a statement released Wednesday evening, the prosecutor's office said its investigation indicated a link between the poisoning of Litvinenko and criminal cases under way against Yukos executives. It singled out Leonid B. Nevzlin, a major shareholder and partner of the company's jailed chief executive, Mikhail B. Khodorkovsky.

The statement did not elaborate on any evidence that might link Nevzlin and others to Litvinenko's death, which was caused by a lethal dose of a radioactive material, polonium 210.

The accusation nevertheless was an effort on the part of the Russian government to tie Litvinenko's death to accusations of a convoluted web of economic and other crimes that destroyed Yukos, once Russia's richest company.

The prosecution of Yukos and Khodorkovsky was widely seen as a Kremlin-led campaign against a company seen as defiant of President Vladimir V. Putin and against a man seen as a potential political threat.

A spokesman for Nevzlin, a close associate of Khodorkovsky's who is wanted on charges in Russia and lives in self-imposed exile in Israel, dismissed the new accusations as a continuation of that campaign.

"We all know the methods of the KGB," the spokesman, Amir Dan, said in a telephone interview, referring to the defunct Soviet security agency. "The statement is ridiculous. It is not worth any comment."

When Litvinenko fell ill on Nov. 1, officials in Russia ridiculed the accusations of Russian involvement. But when he died on Nov. 23 from the effects of radioactive poisoning, investigators here agreed to assist British detectives, who visited for several days this month.

The statement from the Prosecutor General's Office said the investigations of Yukos had now been combined with that of Litvinenko's death.

"A version is being verified according to which the contractors of these crimes may be one and the same group of people whose names are on the international wanted list" for committing grave crimes, the prosecutors' statement said. It specified Nevzlin as one of them but did not identify any others.

Nevzlin has long evaded Russian requests for extradition — a source of diplomatic irritation between Russia and Israel. On Sunday he arrived in the United States on vacation, Dan said, prompting new demands by the Russians that the Americans arrest him.

A U.S. government official who has been briefed on the case and spoke on condition of anonymity because of privacy regulations said Nevzlin had arrived at Newark Liberty International Airport in New Jersey on Dec. 24 and had been questioned by Customs and Border Protection officers. He had a valid visa and was allowed into the country, the official said. A Justice Department spokesman said the department had no information about Nevzlin.

The prosecutors' statement said Russia would prepare new requests for extradition, though it did not identify the countries to which the requests would be made.

Nevzlin's name has surfaced in connection with the Litvinenko case before. He met with Litvinenko in the weeks before his poisoning, evidently in October. After Litvinenko's death, Nevzlin said that Litvinenko had provided him with a dossier that "shed light on most significant aspects of the Yukos affair."

The dossier's contents remain unclear, but Nevzlin said he had provided them to British investigators. It was also unclear how Litvinenko, who fled Russia in 2000, could have come to possess incriminating information about a case that unfolded after his departure.

The investigation of Litvinenko's death has spread beyond Britain. In Germany investigators discovered traces of polonium at places visited by Dmitry V. Kovtun, another businessman and former security officer who was one of two Russian businessmen who met Litvinenko in London on Nov. 1, the day he was evidently poisoned.

The traces found in Germany appeared to have been left in the days before he flew from Hamburg to London on that morning.

Prosecutors here say they are investigating Kovtun's poisoning as an attempted murder committed in conjunction with Litvinenko's killing. That would suggest that Kovtun was a victim, not a suspect.

Kovtun is said to be in a Moscow hospital being monitored for symptoms of radiation poisoning, though his condition and whereabouts are shrouded in mystery. He and the other businessman, Andrei K. Lugovoi, were questioned by Russian and British investigators. Nothing is known of the nature of their responses.

The man at the center of the Yukos affair, Khodorkovsky, the company's former chairman, has also come under new prosecutorial scrutiny. Convicted last year on charges of fraud and tax evasion that his supporters described as politically motivated, Khodorkovsky was transferred over the weekend from the remote Siberian prison where he is serving an eight-year sentence to a regional detention center in Chita.

On Wednesday prosecutors preparing new criminal charges against him questioned him and his jailed business partner, Platon A. Lebedev, Khodorkovsky's lawyer said in a statement. The lawyer, Yuri M. Schmidt, said investigators accused his client of laundering money by making contributions to Open Russia, a social and educational charity Khodorkovsky founded. The authorities have since closed the charity.

Schmidt said the timing of the new questioning amounted to "moral and physical pressure" on his client, whose current sentence does not end until 2012.