In his statement to reporters, Russian ambassador Alexander Yakovenko also says Russia will not accept any decisions reached in secret and based on evidence not tested in open court.

The length of time taken to come to these conclusions led them to believe it was "a whitewash of British security services incompetence", he adds.

He went on to say that these events "can't help but harm our bilateral relations".

The Guardian has a feature on the Litvinenko case titled "The man who solved his own murder." It features details of the witness statements Alexander Litvinenko gave to police. Read here, external

BBC Monitoring

The Russian ambassador in the UK, Alexander Yakovenko, rejects the outcome of the Litvinenko inquiry.

"It is absolutely unacceptable for us that the report contains the conclusion that the Russian state is somehow involved in Litvinenko's death on British soil," he says after being summoned by the Foreign Office in London.

Shadow home secretary Andy Burnham has described the murder of Alexander Litvinenko as an "act of state-sanctioned terrorism": 

Senior Conservative MP David Davis, who was shadow home secretary when Mr Litvinenko was murdered, says the government needs to take firm action against Russia.

A host of names linked to the Litvinenko case have been mentioned throughout the morning. Here is some background on some of those individuals.

Image source, AP

Alexander Litvinenko: A Russian soldier, who became a spy at the Soviet intelligence agency, the KGB (later the Federal Security Services, or FSB). 

After falling out with Vladimir Putin, then his boss at the FSB, he fled to the UK where he eventually became a British citizen and began working for MI6. 

He was murdered in London in 2006. Read a full profile here.

Image source, AFP

Nikolai Patrushev: Currently the secretary of the Security Council of Russia. He was director of the FSB, during Vladimir Putin's first two terms as president (1999-2008) and was very close to him.

Inquiry chairman Sir Robert Owen said: "Taking full account of all the evidence and analysis available to me, I find that the FSB operation to kill Litvinenko was probably approved by Mr Patrushev and also by President Putin."  

Mr Patrushev said last year in an interview with a Russian newspaper that the United States "really would like it if Russia did not exist at all as a state".

Image source, Getty

Andrei Lugovoi and Dmitry Kovtun: For many years, these two Russians have been the chief suspects in Mr Litvinenko's murder. 

Mr Lugovoi had been in the FSB and the federal protection service, and continued to have strong links to the FSB.

Mr Kovtun is a former Soviet army officer who has said he was at one point a member of the Russian army intelligence corps. He announced in March that he wanted to testify to the inquiry, but later said he would communicate only via email.

Both have denied any involvement in the murder, and there has been no sign that they will be extradited from Russia to face charges in the UK.

Read a full profile here.  

Image source, EPA

Vladimir Putin: According to the Kremlin website, external, Mr Putin wanted to work in Soviet intelligence "even before he finished school".  

He served as a spy in communist East Germany - with some of his ex-KGB comrades later receiving top state posts when he became president.

He entered Boris Yeltsin's Kremlin in 1997, and was made chief of the Federal Security Service, and then prime minister, and finally president in 1999.

During his presidential period, many of his critics have been exiled abroad.

The Litvinenko inquiry concluded that he "probably" approved the assassination of Alexander Litvinenko, one of his vocal critics, because of personal "antagonism" between them.

Read a full profile here.

Andrei Lugovoi and Dmitry Kovtun have long been named by British police as prime suspects but attempts to extradite them from Russia have failed. They have always denied any involvement. Read our profile of the men

BBC Monitoring

Dmitry Kovtun, one of the men suspected of killing Alexander Litvinenko, again denies involvement.

"I am not involved in Litvinenko's death. As for the outcome of the public inquiry that has been published in London, Robert Owen could not have reached any other conclusions based on the falsified and fabricated evidence," he tells Interfax.

Here's how our news story has captured today's events:

The murder of ex-Russian spy Alexander Litvinenko in 2006 in the UK was 'probably' approved by President Vladimir Putin, an inquiry has found.

Mr Putin is likely to have signed off the poisoning of Mr Litvinenko with polonium-210 in part due to personal "antagonism" between the pair, it said, external.

Home Secretary Theresa May said the murder was a "blatant and unacceptable" breach of international law.

But the Russian Foreign Ministry said the public inquiry was "politicised".

It said: "We regret that the purely criminal case was politicised and overshadowed the general atmosphere of bilateral relations."

Mr Litvinenko's widow Marina welcomed the report, calling for sanctions to be imposed on Russia and a travel ban on Mr Putin.

Her husband died aged 43 in London in 2006, days after drinking tea poisoned with the radioactive substance.

The former Russian spy - who is believed to have later worked for MI6 - had been a fierce critic of the Kremlin.

Read the full story here

We have plenty of background material available on the Litvinenko case including this piece on his family's long road to the truth, which was written ahead of today's inquiry findings.

Analysis by Gordon Corera, BBC security correspondent

The conclusions of this inquiry are stronger than many expected in pointing the finger at Vladimir Putin personally - although the evidence behind that seems to have come from secret intelligence heard in closed session.

Saying that Alexander Litvinenko was killed because he was an enemy of the Russian state will raise pressure on the British government to take real action - the steps taken nearly a decade ago were only limited in scope.

That may be pose difficulties given the importance of Russia's role in the Middle East but, without tough action, people may ask if the Russian government has been allowed to get away with what's been described as an act of nuclear terrorism on the streets of London.