Britain said it would launch a formal inquiry into the death seven years ago of ex-Russian spy Alexander Litvinenko, but they said it has nothing to do with suspected Russian involvement in the downing of Malaysia Airlines Flight 17 in Ukraine last week.
Prime Minister David Cameron's spokesman said there is "no link whatsoever" between flight MH17 and Tuesday's announcement.
Litvinenko was a former Russian spy who died after drinking radioactive polonium-210 in his tea at a London hotel in 2006. The British investigated Litvinenko's death at the time, without deciding whether the Russian state itself might have been to blame for the murder.
Litvinenko broke ranks with his government and on his deathbed accused Russian President Vladimir Putin of ordering his murder.
The decision to launch a formal inquiry represents a major turnaround for the British government. It had previously resisted a formal inquiry on the grounds that it did not want to make public sensitive intelligence information.
The inquiry will begin July 31 and is expected to last until the end of 2015.