TIMELINE-The case of poisoned ex-spy Alexander Litvinenko

(Reuters) - Russia said on Thursday it would expel four British diplomats from Moscow in retaliation for Britain's decision earlier this week to send home four Russian diplomats.

The British move came after Moscow refused to extradite Andrei Lugovoy, main suspect in the murder last year of Alexander Litvinenko, a former Russian intelligence officer living in Britain.

Here is a timeline of events:

November 1, 2006 - Litvinenko complains of feeling unwell after a day spent with contacts. After meeting the Italian Mario Scaramella at a sushi bar in Piccadilly, he saw former KGB contacts Lugovoy and Dmitry Kovtun at the Millennium Hotel. Traces of radiation were later found at both places.

November 23 - Litvinenko dies of radiation poisoning. Traces of polonium-210 are found in his system.

November 24 - Litvinenko accuses Russian President Vladimir Putin of his murder in a statement read out by friends the morning after his death. Putin brushes off the accusation.

November 28 - Prime Minister Tony Blair promises that "no diplomatic or political barrier" will be allowed to hamper the investigation into Litvinenko's death.

December 1 - Pathologists carry out a post mortem on Litvinenko's body.

-- Scaramella is admitted to hospital in London and traces of polonium-210 are also found in the urine of Litvinenko's widow Marina. Scaramella leaves hospital on December 6.