Russia will not extradite suspects in the poisoning of ex-spy Alexander Litvinenko to Britain, the country's prosecutor general has said.
Russia will not extradite suspects in the Litvinenko case
Yuri Chaika said any trial of a Russian citizen must take place in Russia.
Nine British police officers are currently in Moscow pursuing inquiries into Mr Litvinenko's death.
But Mr Chaika told a Moscow news conference that arrests of Russians by British officers would be "impossible" under the Russian constitution.
In a further development, the AFP news agency has reported that Mr Litvinenko will be buried on Friday in a Muslim ceremony.
The ex-spy's father, Walter, said his son would be buried in a Muslim graveyard in or near London. He added family and Muslim friends would be present.
"It will be quite a special funeral, you understand, the coffin will be closed," he told the agency.
Mr Chaika said there will not be any trade between Britain and Russia of wanted figures over the death of the former KGB agent.
He also dismissed the claim that the highly toxic isotope polonium-210, which is being linked to Mr Litvinenko's death, was produced in Russia.
He said British authorities have not asked for help in tracing the source of the radioactive substance.
"I believe there is no need to conduct such an investigation in Russia. Why do you think then that it was not Britain that produced it?" he said.
British police launched their investigation after Mr Litvinenko, 43, died in a London hospital on 23 November.
Tests have been carried out at a number of venues the ex-spy visited in London on November 1 - the day he fell ill.
A hotel and an office are the latest central London locations to be tested for signs of the deadly toxin found in the ex-KGB agent's body.
A room at the British Embassy in Moscow is also being tested as a precaution.
On Monday, officers from the Metropolitan Police's counter-terrorism command arrived in the Russian capital to pursue their inquiries.
Home Secretary John Reid said officers would "follow the evidence" as Russia warned speculation on the death was harming relations with the UK.
BBC correspondent James Rogers said Russian authorities have so far co-operated with the British police, but that comments made by Mr Chaika throw into question just how far their co-operation will go.
Russian prosecutors have said they intend to question former KGB bodyguard Andrei Lugovoi, who met Mr Litvinenko in London on 1 November.
Mr Lugovoi has said he was expecting to meet with British police in the coming days.
Andrei Lugovoi has denied any involvement in the poisoning
He added that he had been undergoing tests in a Russian hospital for possible radiation poisoning.
"If they show me a list of people that they want to meet and if there are names missing on that list, names that I believe would be interesting to propose to them, then I certainly will," he told NTV television.
Mr Lugovoi is one of three Russian businessmen reported to have met Mr Litvinenko on that date.
But one of them, Vyacheslav Sokolenko, has denied he ever had any contact with the former KGB agent.
Vyacheslav Sokolenko told BBC Moscow he was in London, but only to watch the football.
He says Mr Lugovoi and Dmitry Kovtun met Mr Litvinenko, but he was not present, adding he never knew the ex-spy.
Friends believe Mr Litvinenko was poisoned because of his criticisms of the Russian government, but the Kremlin has dismissed suggestions it was involved in any way as "sheer nonsense".
Meanwhile, Mario Scaramella - an Italian contact of Mr Litvinenko's who also met him on the day he fell ill - is still being observed by doctors after testing positive for polonium-210.
So far more than 3,000 people in the UK have called the NHS Direct line since the radiation scare, with 179 being followed up for further investigation, the HPA said.