Rogue hit squad may have killed ex-spy

London/Moscow: Detectives are to fly to Moscow and Rome this week in an attempt to unravel the mysterious radioactive poisoning in London of former Russian spy Alexander Litvinenko.

Senior security sources in Britain suspect that Russian agents - possibly a rogue unit - were behind the sophisticated nuclear weapons element used to commit the murder.

Scotland Yard's Counter Terrorism Command wants to question two Russians and an Italian professor who lunched with Litvinenko at the same Japanese restaurant in central London, just two weeks apart. On Saturday, the professor said he feared for his life.

Detectives have pinpointed Itsu, a sushi restaurant in Piccadilly, London, as the most likely place that the former KGB colonel was poisoned with polonium-210, a radioactive metal element used to trigger nuclear weapons.

The restaurant was sealed off after radiation was detected in several places. Itsu was a regular eating haunt for Litvinenko, one of the fiercest critics of the Russian president Vladimir Putin.

Litvinenko, 44, died on Thursday night with his family at his bedside.

It was known that he had met a contact - an Italian defence consultant called Professor Mario Scaramella - at Itsu on November 1. The Italian had information on the death of Anna Politkovskaya, 48, the Russian investigative journalist murdered last month. Detectives also learnt that Litvinenko went on from his lunch with Scaramella to see two Russians, Andrei Lugovoy and Dimitri Kovtun, at the nearby Millennium Hotel, at 4pm. The hotel has also been sealed off after further traces of radiation were found.

Itsu was also the venue for a lunch the Russian defector had two weeks earlier, on October 16, with the two Russians. The men had a further meeting with Litvinenko, this time at a restaurant in Soho's Chinatown, a day later to discuss a "business deal".

Scotland Yard officers will fly to Moscow, possibly as early as tomorrow, to interview Lugovoy and Kovtun, who have said they will co-operate with the investigation.

Detectives will also travel to Rome to see Scaramella. The Italian defence consultant is expected to tell officers that he was with the murder victim for some 45 minutes. He apparently saw Litvinenko help himself to fish from a buffet and was brought soup by a waiter.

Scaramella said: "Litvinenko did not die from a stomach ache. He was killed because of what he knew. There is no doubt that the Kremlin killed Litvinenko. I am now in fear of my life."

Litvinenko's widow Marina, also 44, his 12-year-old son Anatoly, and father Walter all face a troubling 48 hours until they learn whether their bodies have been contaminated with polonium 210 as a result of their contact with their dying relative.

Friends believe that Litvinenko was killed by the Federal Security Bureau, the successor to the KGB. They suspect Putin of ordering his death, but others consider rogue elements in the bureau were responsible using the sophisticated poison which is difficult to make and obtain.