Four people -- three employees at London hotels and a Swedish visitor -- have tested positive for the radioactive element that killed former Russian spy Alexander Litvinenko, authorities said Tuesday.

Tests on two staff members at the Millennium Hotel in central London and on one at the Sheraton Hotel have shown exposure to polonium-210, Britain's Health Protection Agency said.

Sweden's National Board of Health and Welfare said a Swede who had visited one of the hotels had "slightly elevated" levels of polonium.

The level of the radioactive substance was not harmful to the Swede's health, and test results could not explain what caused the higher-than-normal level, the board said.

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"The level is so low that it theoretically could have been caused by cigarette smoke or eating certain foods," said Jonas Holst, an expert at the board. "But since this person has been in London that is of course a possible explanation for the elevated levels."

Holst said the Swede had visited one of the hotels -- which he did not identify -- where British investigators had found traces of the radioactive element.

Other Swedes had also been tested but did not show any elevated levels of the substance, he said.

Litvinenko died Nov. 23 in London after being poisoned with polonium-210 and in a deathbed accusation blamed Russian President Vladimir Putin for his death -- an allegation the Kremlin vehemently denied.

A total of 10 people in Britain have now been exposed to radiation in Britain since Litvinenko's death.

Previously one member of the former spy's family -- his wife Marina -- and seven members of staff at the Millennium Hotel's bar had tested positive. However, one of the hotel workers was later found to have normal radiation levels.

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