The poisoning of Russian spy Alexander Litvinenko would be "state-sponsored nuclear terrorism on the streets of London" if it were proved foreign agents were behind his death, the lawyer for his wife has said.
The comments came as reports emerged that parts of a police report on whether Litvinenko had contact with the British intelligence service before he died would be kept secret at the government's request.
The Metropolitan Police investigated whether Litvinenko was in touch with MI6 prior to his death, a pre-inquest review hearing was told.
Litvinenko, 43, was poisoned with polonium-210 while drinking tea at a meeting, allegedly with two Russians - former KGB contacts Andrei Lugovoy and Dmitry Kovtun - at the Millennium Hotel in London's Grosvenor Square.
Ben Emmerson QC, for Marina Litvinenko, the murdered Russian's wife, said wanted to know whether her husband's death was "a targeted assassination of a British citizen committed by agents of a foreign state in the sovereign territory of the United Kingdom".
Counsel for the inquest Hugh Davies said the contents of the secret police report are known to his team and to the coroner, Sir Robert Owen.
However, they will not be disclosed to the other interested parties represented at the inquest, at the request of the government.
Mr Davies said: "Claims have been made to the effect that Mr Litvinenko had contact with British intelligence service prior to his death. As part of its investigation, the Metropolitan Police Service made an inquiry into these claims.
"Pending the outcome of the disclosure exercise currently under way, the product of these inquiries which are known to you sir, and counsel and solicitors to the inquest, has been redacted from the report at the request of Her Majesty's government.
"This redaction, of course, should not be taken as indicating one way or the other whether Mr Litvinenko did indeed have any such contact."
At the start of today's hearing, held to establish how the inquest will be conducted, Sir Robert said: "It has been almost six years since his death in November 2006. Such a delay is regrettable.
"There will be no further delay. It is manifestly in the interests of the interested persons, in particular his widow Marina Litvinenko and his son Anatoli Litvinenko, of the other interested persons and in the wider public interest that the inquest is brought to a conclusion with due expedition.
"It's my intention to commence the substantive hearings at the first practicable opportunity as early in 2013 as is consistent with the completion of the necessary preparatory steps."
The next preparatory hearings for the inquest will take place on November 2 and December 13 and 14.