Police refused to comment on the report, which said an investigation by the Radiological Protection Institution of Ireland (RPII), on behalf of the police, had found no traces of radiation in places visited by Gaidar.

The Irish Independent said the RPII tests were carried out at the National University of Ireland at Maynooth, west of Dublin, where Gaidar was a guest speaker on November 24, and at the James Connolly Memorial Hospital in nearby Blanchardstown, where he was medically treated after taking ill.

"Medical staff at the hospital say Mr Gaidar had been suffering from the early effects of gastro-enteritis and was treated for that condition.

"They found no indication that Mr Gaidar had been poisoned or was suffering from any form of radiation," the newspaper said.

The report said senior police officers had been sceptical of the poison claims from the start but decided on an investigation to allay public concern that other people might be contaminated by radiation.

Gaidar's illness came one day after the death in London of former Russian secret service agent Alexander Litvinenko, who was poisoned by the radioactive isotope polonium-210 in an incident that Litvinenko himself blamed on Russian President Vladimir Putin's regime.

The Independent said that all lines of the police inquiry indicate "that there is no link between Mr Gaidar's illness and the death of Mr Litvinenko."

The former acting prime minister's mother, Arianna Gaidar, has linked her son's illness to hypertension, according to a report in the Irish Times newspaper.

She said she was very shocked to learn that her son might have been poisoned.

Her family had avoided telling her for some time, so as not to distress her. But she made it clear she still hoped there could be a different explanation.

"I hope that it was hypertension. He was after flying a lot, tired and there were all the pressure changes," she said. "When there will be a final diagnosis, I hope that we will calm down," she told the newspaper.

The Irish Times said her comments differ from those of Gaidar's daughter Maria, who claimed that since Russian doctors could not discover the cause of his illness, they had concluded that he must have been poisoned.

"Ms Gaidar, a political activist in Russia, was arrested at a protest rally on the day Dr Gaidar travelled to Ireland. It is believed he was very concerned about her welfare at the time," the newspaper said.