Police in Germany said traces of polonium-210, the radioactive element that killed Litvinenko, had been found at two Hamburg-area homes linked to a contact of the ex-KGB officer.
At London's Millennium Hotel in Mayfair — where Litvinenko drank tea with a group of fellow Russians and where he appears to have been fatally poisoned — officers reportedly were testing a cup and a dishwasher for traces of the toxin.
In Moscow, prosecutors said officials would travel to Britain as part of a Russian inquiry into the killing, but did not confirm who would be questioned or when the interviews would take place.
Andrei Nekrasov, a friend of Litvinenko, said there was concern among emigres in the British capital that the Kremlin would use the inquiries as a "pretext to harass exiles in London."
German police said Saturday they had found traces of radiation at two Hamburg area homes linked to Dmitry Kovtun, a Russian businessman present at the London hotel meeting and later hospitalized with polonium contamination.
Traces were found at his ex-wife's Hamburg apartment, and an initial scan also yielded signs of contamination at Kovtun's former mother-in-law's home in Haselau, west of the port city, Hamburg police said.
In additrion, German airline Germanwings said Saturday that an aircraft on board which a contact of dead Russian spy Alexander Litvinenko flew to London was being tested for possible traces of the radioactive substance polonium-210.
Germanwings said it took the Airbus A-319 out of service at Cologne-Bonn airport after receiving information from authorities that Dmitry Kovtun flew to London from Hamburg on the plane on Nov. 1. Kovtun met with Litvinenko later that day.
Litvinenko, 43, died in London on Nov. 23 after blaming President Vladimir Putin in a deathbed message — an accusation the Kremlin has vehemently denied.
A spokeswoman for Moscow's Prosecutor General's office, who said she was not authorized to give her name to media outlets, told The Associated Press there were plans to send Russian investigators to London.
She said it was unclear when they would make the trip. "There is no concrete date," she said.
British police said they had no details of the planned visit by Russian investigators and it was not immediately clear whether they would be given access to exiles granted political asylum by the British government.
Exiles in London were worried about the arrival of Russian officials, and feared their motive could be to unsettle the emigre community, Nekrasov said.
He said that former Russian security officer Mikhail Trepashkin, serving a four-year prison sentence after being convicted of divulging state secrets, had said a Kremlin agent previously ordered to monitor Litvinenko was among those appointed to investigate the killing.
Investigations in Britain have focused on the Pine Bar at London's Millennium Hotel, where Litvinenko held a morning meeting over tea and gin with three fellow Russians on Nov. 1 — the day he fell ill.
Britain's Daily Telegraph newspaper said police were testing a tea cup and dishwasher at the hotel for signs of radiation. Officials said they could not immediately comment on the report.
Andrei Lugovoi, also an ex-Soviet agent, Kovtun and Vyacheslav Sokolenko, the head of a private Russian security firm, joined the meeting in the hotel's intimate, blond oak-paneled bar.
All three have denied involvement in the ex-spy's death.
Intelligence analyst Glenmore Trenear-Harvey told CBS's Saturday Early Show, "Isn't it extraordinary — we have moved from a Cold War/La Carre to something out of an Agatha Christie whodunit, because the suspect is an old-fashioned English cup of tea."
"The fact is, wherever Lugovoi has been, he has left in his wake a scattering of polonium-210," Trenear-Harvey said. "He is either a perpetrator or one of the most unfortunate victims himself."
Trenear-Harvey pointed to Litivenenko's past in counter-intelligence, and then in internal affairs, where he made enemies, as a possible motive for his poisoning.
"It was his role to root out corruption and coercion within the intelligence services [and] he found it in squads. But did he make enemies — he has so many."
All seven staff working at the bar on Nov. 1 showed evidence of exposure to polonium-210, Britain's Health Protection Agency said. Kovtun and Scaramella both have fallen ill since the meeting.
Dr. Michael Clark of the Health Protection Agency said it was likely the poisoning occurred at the hotel bar. He said food, drinks and cigarettes all could have been used to hide the poison.
Polonium is so dangerous that a lethal dose would occupy a space just 100 micrometers across — slightly larger than the point of a pin. Though polonium-210 is available by mail, one vendor in New Mexico, Bob Lazar, said such small amounts are sold that 15,000 orders would be needed to potentially harm someone.
Around 200 other people who visited the hotel bar on Nov. 1 were being contacted and offered tests, British health officials said.
Scaramella was hospitalized last week in London. He said doctors told him he had received five times the lethal dose of polonium-210, although he showed no symptoms. He left the hospital Wednesday.
In Moscow, Kovtun had "developed an illness also connected with the radioactive nuclide (substance)," Russian prosecutors said. Lugovoi was tested for radiation poisoning in a hospital, and Russia's Interfax news agency said he showed signs of contamination.