(AFP) - British detectives were in Moscow to continue their investigation into the mysterious poisoning death of former spy Alexander Litvinenko, as diplomatic tensions between Britain and Russia rose closer to the surface.
A spokesman for the Metropolitan Police confirmed that "a team of officers" had arrived in Moscow, but could not say how many had made the trip, or how long they planned to stay, reports Trend.
While British media have reported that nine detectives went to Moscow, Russian state television RIA-Novosti said that only four arrived, and were met by British embassy offiicals before leaving in a minivan.
According to The Guardian daily, the officers were to interview the three Russian men who met Litvinenko on November 1, the day he fell ill, about three weeks before he eventually died. They will also interview two men whose names have not yet appeared publicly, the newspaper said.
The trio -- businessmen Andrei Lugovoi, Dmitri Kovtun and Vyacheslav Sokolenko -- have all asserted that they are innocent, and Lugovoi has said that he believes they are being framed. In comments made to The Times, he said he and his two associates were ready to meet with investigators.
Meanwhile, lawyers for jailed former Federal Security Service (FSB) agent, and acquaintance of Litvinenko, Mikhail Trepashkin, have said he has key evidence in the case, and have urged the detectives in Moscow to meet with their client.
Alex Goldfarb, a close friend of Litvinenko, said that Trepashkin's health was poor and warned that if police did not visit with him in jail in eastern Russia, they could miss out on an "important witness".
"He knows those old boys who are mad at Alexander for defecting," Goldfarb said.
The Times reported on Tuesday that British intelligence officers are convinced that the Russian secret service authorised Litvinenko's poisoning, citing unnamed security sources.
According to the report, only officials such as agents of the FSB would have access to sufficient amounts of the radioactive substance polonium-210 to kill Litvinenko. The former agent's urine was found to have large unexplained quantities of the isotope. Meanwhile, one room in the British embassy in Moscow is to be tested for radiation "in the next day or so", a spokesman for the British foreign ministry told AFP on Monday. He described the tests as "precautionary".
In Britain, authorities extended their search for radioactive material to two more buildings in central London -- in addition to the dozen or so that have already been examined -- the Health Protection Agency said.
The political fall-out of the investigation into Litvinenko's death has also seemingly strained relations between London and Moscow, with Russian Foreign Minister Sergei Lavrov saying on Monday that it was "unacceptable that a campaign should be whipped up with the participation of officials."
"This is of course harming our relations," Lavrov was quoted by Interfax news agency as saying during a visit to Brussels.
The Guardian reported on Tuesday that as there is no bilateral extradition treaty between Britain and Russia, any one-off extradition request for a Russian suspect to be sent to Britain to stand trial would require Russian parliamentary approval.
According to the newspaper's report, Russia granted itself an exemption to a 1996 European convention on extradition which it signed in the form of an amendment to its constitution which reads: "A Russian citizen cannot be sent beyond the borders of the Russian Federation or given to another state."
In what some suspect to be a related case of poisoning, former Russian prime minister Yegor Gaidar was released from hospital on Monday, after having been stricken with an unexplained illness 10 days ago, the Interfax news agency reported, quoting his spokesman.
In another unexpected development in the story, Litvinenko's father said his son had requested before his death that he be buried according to Muslim tradition.
"He converted to Islam when he was sick, at a point when he didn't yet know he was going to die," Valter Litvinenko told AFP by telephone, confirming a Russian press report.
"My son voiced the wish to be buried following Muslim custom."
One of Litvinenko's contacts, Mario Scaramella, meanwhile said he was confident that polonium-210 found in his body had not led to "a degeneration of internal organs".
Scaramella told Italian news agency ANSA that doctors at London's University College Hospital would continue to keep an eye on him.
He had said on Italian state television Sunday that he had five times the amount of the radioactive substance considered deadly in his body.
But the hospital said Monday further tests were being carried out and that there was no evidence to suggest the level was five times the amount considered deadly.