British detectives who went to Moscow to investigate the murder of Alexander Litvinenko have returned to the UK, Scotland Yard has said.
Alexander Litvinenko died in a London hospital last month
Officers went to Russia as part of the inquiry into the death of the ex-KGB spy, thought to have been poisoned with radioactive isotope polonium-210.
They reportedly interviewed two Russian men who allegedly met Mr Litvinenko in London on the day he fell ill.
Agencies have started cleaning sites in London where polonium-210 was found.
In a statement on Wednesday, Scotland Yard said: "The team of Metropolitan Police officers who carried out a number of inquiries in Moscow into the death of Alexander Litvinenko have now returned to London.
"The team have worked closely with the prosecutor general's office in Moscow and the team have thanked the office for its co-operation.
"The investigation continues and we are following all lines of inquiry."
A spokesman for the force said the British officers had received "satisfactory co-operation" from the Russian authorities.
Mr Litvinenko, 43, died in University College Hospital, London, last month.
On his deathbed he accused Russian President Vladimir Putin of being behind his poisoning. Moscow has denied any involvement.
It emerged that he met two Russian men at the Millennium Hotel, London, on 1 November, the day he fell ill.
The men he is thought to have met, Dmitry Kovtun and Andrei Lugovoi, were reportedly interviewed by the Scotland Yard team in Russia.
During the investigation into his death 30 sites across the capital, including aircraft, were identified as being actually or potentially contaminated with polonium-210.
The majority have since been declared safe for public use.
It was announced on Wednesday that agencies led by Westminster City Council have begun the task of cleaning up the remaining locations.
The council has said it will arrange for independent checks to verify the work has been completed.
Westminster City Council's chief executive, Peter Rogers, said: "Every step in this process has been taken with public safety paramount in our concerns.
"By combining due speed and minimal risk we hope to resolve this issue as quickly, and as safely, as possible."