An inquest into former spy Alexander Litvinenko's death will examine claims the Russian government was involved.
Counsel for his widow Marina told a hearing if proven this would be an "act of state-sponsored nuclear terrorism".
Mr Litvinenko, 43, is thought to have been poisoned with polonium-210 after meeting two Russians for tea at a central London hotel in November 2006.
Sir Robert Owen said the full inquest would take place in early 2013.
Parts of a police report into Mr Litvinenko's death will be withheld to omit a section about his alleged links to British intelligence.
Prime suspect Andrei Lugovoi has since been elected as a Russian MP.
Ben Emmerson QC, counsel for Mr Litvinenko's widow Marina, said they believed Russia was responsible.
"If that hypothesis were to be evidentially substantiated, this would be an act of state-sponsored nuclear terrorism on the streets of London."
The death of Mr Litvinenko, a former Russian security officer who had obtained asylum in Britain, led to a major diplomatic incident in 2006 as the Kremlin was accused of masterminding his murder.
Thursday's pre-inquest review hearing was told "interested parties" would receive a summary of Scotland Yard's investigation report into Mr Litvinenko's death but certain intelligence reports would be withheld, including where the Metropolitan Police was asked to examine any links between Mr Litvinenko and British intelligence.
Counsel to the inquest, Hugh Davies, said: "This redaction, of course, should not be taken as indicating one way or the other whether Mr Litvinenko did indeed have any such contact."
He said all competing theories would be examined, adding: "The court is committed to transparency."
Mr Emmerson said Mrs Litvinenko "is keen that the significance of all the evidence, including that which is redacted, is in one way or another fairly and independently evaluated and that as much as is possible should be made public".
He said she wanted to know if it was "a targeted assassination of a British citizen committed by agents of a foreign state in the sovereign territory of the United Kingdom".
Mr Davies said some foreign witnesses could give evidence by video link.
Mr Lugovoi is represented as an interested person but Dimitri Kovtun, another Russian former agent who was present at a meeting with Mr Litvinenko on 1 November 2006, is not.
Others with interested person status include Home Secretary Theresa May, Mrs Litvinenko and her son Anatoli, and Russian tycoon Boris Berezvosky.
Sir Robert, a High Court judge appointed as an assistant deputy coroner for the inquest, apologised for its delay saying there would be no further delay.
A website has been launched for the inquest, which gives details on the process and lawyers' biographies.
British prosecutors named Mr Lugovoi as the main suspect but he was later elected as a Russian MP and Moscow refused to send him to the UK for questioning. He has denied involvement.
Prime Minister David Cameron raised the issue with Russian President Vladimir Putin during his recent visit to London.
Earlier this year the then Justice Secretary, Ken Clarke, wrote to the then coroner asking for clarification about the estimated £4m inquest costs.