MOSCOW — Russia's chief prosecutor said Tuesday that a potential suspect in the London poisoning death of dissident former KGB agent Alexander Litvinenko had been hospitalized and that British investigators would be allowed to see him only if doctors approved.
Prosecutor General Yuri Chaika also said that Russia's constitution forbade the extradition of citizens and that if any Russians were identified as suspects in the case they would not be sent to Britain and could be tried only in Russia.
Despite earlier top-level pledges of Russian cooperation in the case, Chaika indicated that British investigators might face formidable obstacles pursuing leads in Russia.
Former KGB agent Andrei Lugovoy, who met with Litvinenko in London on the day he was thought to have been radioactively poisoned, had expressed willingness to speak to investigators. But on Tuesday a man answering Lugovoy's cellphone said that it was not clear "whether and when he will be able to talk" to investigators or how long he would remain in the hospital.
The man, who identified himself as an aide named Alexander, said he was not authorized to comment on the nature of Lugovoy's hospitalization. Chaika said he thought Lugovoy was "undergoing medical treatment" but said nothing about his illness.
In a statement written shortly before his death on Nov. 23, Litvinenko blamed Russian President Vladimir V. Putin for his poisoning, a charge the Kremlin angrily dismissed. Litvinenko also told friends that he thought Lugovoy might have been the person who poisoned him.
Chaika, speaking at a news conference, said the questioning of witnesses and potential suspects would be carried out by Russians in the presence of British investigators, who arrived in Moscow on Monday. It was unclear whether British investigators would be allowed to ask questions.
"They will not interrogate anyone," Chaika said at one point. Later he indicated that British investigators might be allowed to ask some questions, with permission, on a case-by-case basis.
"We interrogate and they are present. They interrogate in our presence," he said. "We should perform those investigative actions and they can take part in this with our permission. We may even deny them the right to take part. But we will do this together with them. We want them to take part."
The prosecutor's office has not launched an investigation of its own and will only assist British investigators, Chaika said.
An Italian security consultant, Mario Scaramella, also met Litvinenko on Nov. 1, the day he is believed to have been poisoned with radioactive polonium-210. Scaramella, who authorities say has a "significant quantity" of polonium-210 in his body, said he asked to meet Litvinenko after receiving an e-mail suggesting that the people behind the unsolved slaying of Russian journalist Anna Politkovskaya were preparing to strike against Litvinenko and Scaramella.
Officials in London said they recognized that Russia was one of several nations that as a matter of policy did not extradite its citizens for criminal prosecutions abroad. A spokesman for the Home Office, who spoke under a standard condition of anonymity, said that should a Russian citizen commit an offense in Britain, there are procedures to try the case in Russia.
British Home Secretary John Reid, speaking Monday in Brussels, said the investigation would "proceed as normal, whatever the diplomatic or ... wider considerations."
He said British Foreign Secretary Margaret Beckett "made plain to her Russian colleagues that we are asking them to give us all the support and information that they can."
He said the Kremlin had pledged to cooperate in the investigation. But analysts said Chaika's comments did not seem to indicate there would be complete cooperation.
"The main message Chaika sent to the world today is that there are powerful forces within the Russian political elite which are not interested in an objective investigation of the Litvinenko murder and are not interested in allowing the people who may well be implicated in that crime, like Andrei Lugovoy, for instance, to say something to the British investigators that they shouldn't," said Stanislav Belkovsky, president of the National Strategy Institute, a Moscow think tank.
Valery Fyodorov, director of the All-Russian Center for the Study of Public Opinion, said "the last thing the Russian authorities want now is to look like accomplices in that crime."
"Matters of image are very important for Russia and President Putin, and of course he is willing to help dispel the current gross suspicions in the West," Fyodorov said. "I think that if Scotland Yard representatives happen to claim that they haven't been given due support here in Russia, that may result in the Russian authorities giving Russian law enforcement an additional push and shove."