One of two Russians accused of murdering ex-KGB spy Alexander Litvinenko with a radioactive isotope in London in 2006 can give evidence to a public inquiry into the death after the head of the investigation agreed to give him "core participant" status on Monday.
British authorities believe Kremlin critic Litvinenko was poisoned with green tea laced with polonium-210 at the Millennium Hotel in central London during a meeting with Russians Andrei Lugovoi and Dmitry Kovtun.
Prosecutors say there is enough evidence to charge the men with murder, while before his death, Litvinenko accused Russian President Vladimir Putin of ordering his killing. However, the Kremlin has always denied any involvement, as have Lugovoi and Kovtun, whom Russia has refused to extradite.
Kovtun had initially refused to take part in the inquiry, but in March applied for "core participant" status, which is given to someone who might have played a key role in the events being investigated.
Inquiry chairman Robert Owen announced on Monday he could provide testimony via video-link from Moscow after agreeing to certain conditions.
"Sir Robert is satisfied that Mr Kovtun has complied in full with his directions," said a statement from the inquiry, which began public hearings in January. No date has been set for Kovtun's testimony although it is likely to be towards the end of July.
The inquiry has already been told that while in Germany a month before Litvinenko was poisoned, Kovtun had told a witness he had an expensive poison which he needed a cook to put into the ex-spy's food or drink.
However, Kovtun said in April that Litvinenko, whose death helped drag relations between Moscow and London to new post-Cold War lows, might have killed himself accidentally while handling polonium.
The public inquiry is due to issue its report into the death by the end of the year.