British police said on Wednesday that they were now treating the case of poisoned former Russian spy Alexander Litvinenko as murder.
Detectives had up till now only said that they were treating his death in London from radiation poisoning as suspicious."
Detectives investigating the death of Alexander Litvinenko have reached the stage where it is felt appropriate to treat it as an allegation of murder," Scotland Yard police headquarters said in a statement.
"Detectives in this case are keeping an open mind and methodically following the evidence," it added.
"It is important to stress that we have reached no conclusions as to the means employed, the motive or the identity of those who might be responsible for Mr Litvinenko's death," the statement added.
Menawhile, traces of radiation had been found in the UK's embassy in Moscow.
Detectives on the Litvinenko case who were in Russia intending to interview a number of people, discovered the traces in a search of the building, the Foreign Office said.
An official said there was no threat to public health and embassy staff were working as normal.
A foreign office spokeswoman declined to say what had caused the radiation or where the contamination had been found.
Mr Litvinenko, a fierce critic of President Vladimir Putin, died on November 23rd from radiation poisoning caused by polonium 210.
PA