Britain has announced an inquiry into the death of Alexander Litvinenko, the Russian former spy who accused the Kremlin from his London deathbed of poisoning him with radioactive tea.
The move, which comes as London pushes for greater sanctions against Moscow over the downing of a passenger plane in eastern Ukraine, is likely to anger the Kremlin and further chill relations between the UK and Russia.
The inquiry will be able to look at whether the Russian state was behind the mysterious killing of Kremlin critic Litvinenko in 2006, which outraged Britain at the time and plunged relations with Moscow into the deep freeze.
UK Prime Minister David Cameron's spokesman said there was "no link whatsoever" between the ratcheting up of international pressure on Russia over flight MH17 and the launch of the inquiry.
But it represents a major turnaround for the British government coming just months after it had resisted attempts to hold an inquiry on the grounds of protecting sensitive information about Russian and British intelligence.
"It is more than seven years since Mr Litvinenko's death, and I very much hope that this inquiry will be of some comfort to his widow," said Home Secretary Theresa May, the interior minister, announcing the investigation.
May said the inquiry would specifically seek to identify "where responsibility for the death lies".
'Relieved and delighted'
Litvinenko's widow Marina said she was "relieved and delighted" with the decision, the AFP news agency reported.
"It sends a message to Sasha's murderers: no matter how strong and powerful you are, truth will win out in the end and you will be held accountable for your crimes," Marina said.
"It has taken nearly eight years to bring those culpable for Sasha's murder to justice. I look forward to the day when the truth behind my husband's murder is revealed for the whole world to see."
She said that she too believed there was no link between the timing of the announcement and the tensions with Moscow.
"I do this not against Russia, not England, I do this for justice, I do this for truth ... I'm definitely sure it was not taken because of [the MH17 plane disaster] - the decision to take a public inquiry would have been taken
Litvinenko, an ex-agent in Russia's FSB intelligence agency who turned against his former masters, was poisoned with radioactive polonium-210 while drinking tea at a London hotel.
In a deathbed letter, Litvinenko, who was 43, said he believed Russian President Vladimir Putin was involved in his killing after he publicly criticised the leader, himself an ex-Soviet KGB agent.
British police have identified Russian spy-turned-lawmaker Andrei Lugovoi as the chief suspect and have issued an arrest warrant for his fellow former agent Dmitri Kovtun, but Moscow has refused to hand them over.
They both deny involvement.
The inquiry will begin on July 31 and is expected to run until the end of 2015, AFP said.
Some hearings could be held behind closed doors to examine material which might jeopardise national security, the government said.