Two more people have shown signs of low-level exposure to polonium-210, the rare radioactive isotope that killed former Russian spy Alexander Litvinenko, British health authorities said Wednesday.

The Health Protection Agency said the exposure was too little to cause illness in the short term and the long-term risk was also very small.

The two were identified as a hotel worker at the Best Western Hotel in Piccadilly, London, and a guest who visited The Pine Bar at London's Millennium Hotel.

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Ten other people in Britain have also tested positive for radioactivity, including eight staff members at the Millennium Hotel, one worker at the Sheraton Hotel in Park Lane and Litvinenko's wife Marina.

Litvinenko, a Kremlin critic who lived in exile in London, died in a London hospital on Nov. 23 after suffering radiation poisoning. In a deathbed statement, he accused Russian President Vladimir Putin of ordering his murder, an allegations the Kremlin has denied.

British police say they are treating his death as murder and have conducted investigations in both London and Moscow. Around a dozen London sites have been tested for traces of polonium-210.

A further 536 urine samples tested so far have found nothing of concern, the Health Protection Agency said in a statement.

Detectives are still awaiting the results of the post mortem examination on Litvinenko's body.