British detectives are set to issue arrest warrants for three Russians they suspect killed former Russian agent Alexander Litvinenko, The Mail on Sunday newspaper said.

Police have told sources close to Litvinenko's widow Marina that they intend to charge the trio with murder and poisoning, the weekly said on its front page.

Andrei Lugovoi, Dmitry Kovtun and Vyacheslav Sokolenko, all wealthy businessmen and ex-agents in the former Soviet KGB spying service, met Litvinenko three weeks before his agonising death from radiation poisoning in London last year. They deny any wrongdoing.

The tabloid said the issuing of warrants in the coming weeks would damage already strained relations between Britain and Russia, which would almost certainly block any request for their arrest and extradition.

Britain has refused to heed Moscow's demands for the extradition of oligarch Boris Berezovsky, an outspoken critic of Russian President Vladimir Putin.

Relations between Britain and Russia could deteriorate unless officials in London act against the exiled businessman, Russia's ambassador to Britain said in comments reported Thursday.

Amid the surge in tension between Moscow and Britain, top Russian businessmen and officials have cancelled their attendance at the Russian Economic Forum in London, which starts Monday.

The forum usually attracts major power-brokers who give presentations on Russian business to potential investors.

The Crown Prosecution Service, which oversees criminal prosecutions in England and Wales, told The Mail on Sunday that no decisions had been taken about charges in the Litvinenko case.

Litvinenko -- another outspoken critic of Putin's government and whose associates blame the Kremlin for his death -- died in hospital on November 23, about three weeks after first falling ill.

The 43-year-old was found to have large doses of the highly radioactive isotope polonium 210 in his body.

On November 1, Litvinenko drank tea with Lugovoi and Kovtun, at the Millennium Hotel in central London.

He first complained of feeling unwell later that day after meeting an Italian contact in a nearby sushi restaurant.

Sokolenko also met Litvinenko briefly at the hotel, where investigators have found traces of polonium and a number of staff tested positive for low level radiation contamination.

In December, nine British detectives flew to Moscow. They were not allowed to interview Lugovoi or Kovtun directly, but they were present when Russian police officers questioned them.

They were not granted access to Sokolenko.