Media playback is unsupported on your device Media caption Litvinenko inquiry: What do we know?

The long-awaited findings of a public inquiry into the killing of former Russian spy Alexander Litvinenko are due to be released by a judge.

Mr Litvinenko died aged 43 in London in 2006, days after being poisoned with radioactive polonium-210, which he is believed to have drunk in a cup of tea.

Two Russian men, Andrei Lugovoi and Dmitry Kovtun, have denied killing him.

The judge will decide whether to name any culprits and whether any elements in the Russian state were responsible.

BBC security correspondent Gordon Corera says the real issue for the report is whether the trail leads to the heart of the Russian state and even to President Vladimir Putin himself.

Long road to the truth for Litvinenko family

Who was Alexander Litvinenko?

A deadly trail of polonium

Image copyright AP Image caption Andrei Lugovoi (pictured here in 2006) and Dmitry Kovtun deny involvement

The report may also focus on whether it was specific investigations into links between organised crime and the Kremlin which led to Mr Litvinenko's killing.

I it does point to state responsibility, pressure is likely to grow for the British government to take action against Moscow, our correspondent says.

Speaking ahead of the inquiry's findings, Mr Litvinenko's son, Anatoly, told the BBC: "You want to find out who was behind the murder, who planned it, who commissioned it.

"That is why state responsibility is important to us."

The judge, Sir Robert Owen, heard from 62 witnesses in six months of hearings and was shown secret intelligence evidence about Mr Litvinenko and his links with British intelligence agencies.

Media playback is unsupported on your device Media caption The son of murdered Russian spy Alexander Litvinenko gives his first television interview

The former officer in Russia's FSB spy agency had fled to the UK in 2000, claiming persecution, and was granted asylum. He gained British citizenship several years later.

In the years before his death, he had worked as a writer and journalist, becoming a strong critic of the Kremlin.

It is believed he also worked as a consultant for MI6, specialising in Russian organised crime.

A friend said there was personal animosity between Mr Litvinenko and Mr Putin.

"They disliked each other immensely, because Litvinenko complained about corruption… and Putin shelved his report," Alex Goldfarb said.

"And Putin considered Litvinenko, after the fact, a traitor for going public with his allegations."

The Litvinenko case

23 Nov 2006 - Mr Litvinenko dies three weeks after having tea with former agents Andrei Lugovoi and Dmitri Kovtun in London

22 May 2007 - Britain's director of public prosecutions decides Mr Lugovoi should be charged with his murder

5 Jul 2007 - Russia refuses to extradite Mr Lugovoi, saying its constitution does not allow it

May-July 2013 - The inquest into Mr Litvinenko's death is delayed as the coroner decides a public inquiry would be preferable - but ministers rule out the request

11 Feb 2014 - High Court rules the Home Office was wrong to rule out an inquiry before the outcome of an inquest

January 2015 - Public inquiry begins

Marina Litvinenko, Alexander's widow, and son Anatoly say the report may be a milestone but might not not end their struggle.

"It is important, but it is not necessarily the end", said Mrs Litvinenko, while her son said he felt "a sense of duty".

"My father did a hell of a lot to get me to this country to make sure I was safe," he added.

"I need to respect that and do whatever I can to honour his memory.

"Finding the truth is the closest we can get to justice for my father."