By Bill Smith

London (dpa) - President Vladimir Putin "probably" approved the 2006 killing in London of former Russian spy Alexander Litvinenko, an inquiry in Britain concluded, triggering a row with Moscow.

Former Russian military officer Dmitry Kovtun and a Russian associate, Andrei Lugovoi, poisoned Litvinenko in 2006 under direction from the FSB state security agency, said Robert Owen, the chairman of the government inquiry.

"The FSB operation to kill Mr Litvinenko was probably approved by Mr Patrushev and also by President Putin," he said, referring to Nikolai Patrushev, who was head of the FSB in 2006.

Following a 12-month investigation, Owen said in his report that he was sure Lugovoi and Kovtun were acting under the direction of others when they poisoned Litvinenko, and that both suspects were likely to have been directed by the FSB.

The inquiry and its accusations against the Russian government are "clearly politically motivated," the Foreign Ministry in Moscow said.

"We would like to note that the Russian position on this matter remains unchanged and is well known. We regret that a purely criminal case has been politicized and clouded the overall atmosphere of bilateral relations," spokeswoman Maria Zakharova said, according to state news agency TASS.

Litvinenko, an exiled former spy turned British informant, fled to Britain in 2000 and became an outspoken critic of Putin.

He is believed to have ingested polonium-210, which is produced in nuclear reactors, while drinking tea with Kovtun and Lugovoi in London on November 1, 2006.

British Home Secretary Theresa May told parliament that the finding of Russian state involvement was "deeply disturbing" and reflected "a blatant and unacceptable breach of the most fundamental tenets of international law and civilised behaviour."

The government planned to summon the Russian ambassador and would impose asset freezes against Lugovoi and Kovtun, she said.

Litvinenko's widow, Marina Litvinenko, welcomed the report and urged Prime Minister David Cameron to expel all Russian intelligence officers from Britain and impose "targeted economic sanctions" and travel bans on all Russians linked to her husband's death, including Patrushev and Putin.

British prosecutors had accused Kovtun and Lugovoi of involvement in Litvinenko's murder, but the Russian government refused to extradite them to answer the charges.

Russian officials said again Thursday that they would not extradite the two suspects.

While Moscow planned to present a "detailed review" of the inquiry report after analysing it, according to Interfax news agency, Lugovoi said the allegations against him were "nonsense."

May said she had asked prosecutors to consider whether any more can be done to pursue the extradition of the two men.

London's Metropolitan Police, which led the criminal investigation into Litvinenko's death, said it would continue to seek the arrest of Lugovoi and Kovtun for the "cold and calculated murder" of Litvinenko.

"This has been a painstaking and meticulous [police] enquiry over a number of years that has brought unprecedented challenges requiring an innovative and groundbreaking investigation," said Commander Duncan Ball, who led the police investigation.

Litvinenko was dismissed from his Moscow job in 2000 and was given sanctuary in Britain, becoming a citizen in 2006.

He authored books and articles on Russia's secret services, and once claimed that "all the bloodiest terrorists of the world" had links with Moscow, that they were all trained, funded and armed by the Kremlin to carry out terrorist attacks worldwide.

He also blamed Russia for the 2005 bombings in London in which 56 people died and, in that same year, for the publication of cartoons offensive to Muslims published in a Danish newspaper that led to deadly riots around the world.