An inquiry into the radiation poisoning of a former Russian spy opened on Tuesday with claims that there may have been an earlier assassination bid.

In the most sensational espionage case since the Cold War, Alexander Litvinenko was apparently poisoned by a cup of tea laced with polonium-210 in a London hotel in 2006. He publicly accused Russian President Vladimir Putin of ordering his killing three weeks before his death.

Russia has rejected the accusations and refused to grant extradition for the two chief suspects named by British police - Andrei Lugovoi and Dmitri Kovtun - over the poisoning of Litvinenko on Nov 1 that year.