President Vladimir Putin probably approved a 2006 Russian intelligence operation to murder ex-KGB agent Alexander Litvinenko with radioactive polonium-210 in London, a British inquiry concluded yesterday, sparking a row with Moscow. Litvinenko, 43, an outspoken critic of Putin who fled Russia for Britain six years to the day before he was poisoned, died after drinking laced green tea.An inquiry led by senior British judge Robert Owen found that former KGB bodyguard Andrei Lugovoy and another Russian, Dmitry Kovtun, carried out the killing as part of an operation probably directed by Russia's Federal Security Service."The operation to kill Mr Litvinenko was probably approved by Mr Patrushev, then head of the FSB, and also by President Putin," Owen said.The death of Litvinenko marked a post-Cold War low point in Anglo-Russian relations and ties have never recovered, marred further by Russia's annexation of Crimea and its support for Syrian President Bashar al-Assad."This was a blatant and unacceptable breach of the most fundamental tenets of international law and of civilised behaviour," Interior Minister Theresa May told parliament. The opposition Labour Party spoke of an "unparalleled act of state-sponsored terrorism".The image of Litvinenko lying on his bed at London's University College Hospital, cadaverous and having lost his hair, was emblazoned across Western newspapers and later shown to the inquiry.From his deathbed, Litvinenko told detectives he believed Putin - a former KGB spy who went on to head the FSB before winning the presidency - had directly ordered his killing.The Kremlin has always denied any involvement in the murder. But the claim that Putin directly ordered a killing of an opponent with a radioactive isotope in a major Western capital provoked immediate censure from Moscow.Russia's foreign ministry said what it called Britain's biased and opaque handling of the case had clouded relations.Kremlin spokesman Dmitry Peskov said such inquiries risked poisoning relations and pointed out that the inquiry relied on unpublicised information from the intelligence services.The judge said he was certain Lugovoy and Kovtun had placed the polonium-210 in a teapot at the Millennium Hotel's Pine Bar on November 1 2006 when they met Litvinenko for little more than 30 minutes. Litvinenko said he had only drunk three or four mouthfuls of the cold green tea made with lemon and honey.High polonium contamination was found in the teapot and the hotel bar, and traces of the highly radioactive substance were left across London including offices, hotels, planes and Arsenal soccer club's Emirates Stadium.What is Polonium-210?Polonium-210 is a highly radioactive and extremely toxic material, but to be used as a lethal poison it requires direct contact with a body's inner tissues.A microgram of polonium-210 - the size of a speck of dust - would be sufficient to be a lethal dose.It is a slow and silent killer that attacks the blood cells followed by the liver, kidneys, spleen, bone marrow, gastrointestinal tract and the central nervous system.Polonium-210 is an alpha-emitter, and decays over a period of months.Alpha radiation is absorbed by human tissue so it would have been impossible to detect using a Geiger counter outside of a body. But it does show up in urine.The polonium used to kill Litvinenko would have cost "tens of millions of dollars" if bought on the open commercial market.© The Daily Telegraph..