(CNN) -- A post-mortem examination on the body of poisoned ex-spy Alexander Litvinenko was being carried out at the Royal London Hospital Friday with special precautions being taken because of the nature of his death, reports Trend.
The investigation into the poisoning of Litvinenko, 43, focused increasingly on Moscow after a radiation alert on several aircraft that flew to the Russian capital.
Friends of the former spy said the discovery of radioactivity on British Airways planes reinforced further claims that Russia's security agents were behind the poisoning.
One of those planes, which was grounded at Moscow, was due to fly into London's Heathrow Airport Friday for tests.
British media reports said Culture Secretary Tessa Jowell had taken advice from the Health Protection Agency after learning she travelled on one of the jets at the center of the investigation.
Jowell took a British Airways flight with British Olympics chief Sebastian Coe to Barcelona this month on an Olympics fact-finding visit to the Spanish city.
The Litvinenko investigation meanwhile, gathered pace in London.
The inquest into his death was opened and adjourned at St. Pancras Coroner's Court in north London where Andrew Reid confirmed it appeared as though he had been exposed to, or administered polonium 210.
Home Secretary John Reid revealed that the number of contaminated sites had doubled from six to 12 and was likely to rise again.
The FBI said it had been asked to join the British investigation and that its experts in weapons of mass destruction will assist with some of the scientific analysis.
Meanwhile Irish police announced Thursday they were launching an investigation in to the possible poisoning of Yegor Gaidar, architect of Russia's market reforms. (Full story)
Gaidar, 50, became violently ill and was rushed to a hospital in Ireland, but was improving in a Moscow hospital Thursday.
British Airways has said that "the risk to public health is low," but it has published a list of the flights affected on its Web site and told customers on these flights to contact a special help-line set up by the Health Ministry. (Flight list)
On Friday the airlines said on its Web site that one of the three BA 767s removed from service following the discovery of low traces of a radioactive substance has been given the all clear by UK government agencies.
The Health Protection Agency (HPA) told BA it does not believe that overall passengers on this aircraft -- registration G-BZHA -- were at risk over the past month. This aircraft had flown 72 of the 221 flights identified.
BA said an estimated 33,000 passengers and 3,000 staff were involved in the alert relating to their aircraft, involving the 221 flights to 10 destinations from October 25 to November 29. The airline said it was continuing to make every effort to contact those involved. (Watch how worried you should be about polonium poisoning)
At the opening of Litvinenko's inquest in London Thursday morning, his close friend Alex Goldfarb said the discovery of radioactivity on the BA flights further reinforced his suspicion that Moscow was behind the poisoning.
Ex-KGB man Litvinenko, a fierce critic of Russian President Vladimir Putin, died last week. In his deathbed message, the former spy accused Putin of being behind his poisoning. The Kremlin has denied any responsibility.
Goldfarb told the UK's Press Association: "If you look at the flight numbers BA have released, the first flight they are interested in was five days before the poisoning -- the Moscow-Heathrow flight on October 25.
"This tells you that the police are looking for the ways of delivery of this material into London and this reinforces the theory that the origin of this material that killed Alexander was in Moscow.
"We still believe this is a murder perpetrated by agents of Russia's intelligence services."
Reid said there are between 130 and 150 sites in the United Kingdom where Polonium 210 might be used, but there were no reports of theft from any of the sites.
The Health Protection Agency (HPA) has said the health risk to tens of thousands of air passengers caught up in the radiation alert is likely to be extremely low.
Chief executive Pat Troop said that as alpha radiation cannot pass through skin or even paper, the risk of contamination is "likely to be low."