Russian authorities delayed today a flight by Finnish carrier Finnair from Moscow to Helsinki after detecting radiation on board, Russia's transport ministry said.
"After the plane landed in Moscow's Sheremetyevo airport and all passengers left it, we did some checks and found that the radiation level was above normal. The flight was delayed," a ministry's official said.
The Airbus A319 was due to carry 70 passengers to the Finnish capital and then fly to Berlin.
A Finnair official in Helsinki said the plane would soon get clearance to take passengers aboard.
Russian officials said this week they were on high alert following Britain's decision to monitor several planes for radiation as part of a wider probe into the death from poisoning of a former Russian spy, Alexander Litvinenko.
Radiaiton was detected on three British Airways planes which flew on routes to Russia last week.
Post mortem results on Mr Litvinenko are awaited but the radioactive substance polonium 210 was found in his body. The former spy was a fierce critic of President Vladimir Putin and accused the Russian premier of being behind his killing.
Russia's foreign spy service and many state officials denied any involvement.
Experts yesterday found no traces of radiation at the National University of Ireland in Maynooth after being called in following an incident linked to the death of Mr Litvinenko.
The Radiological Protection Institute of Ireland (RPII) also found no evidence of radiation at James Connolly Memorial Hospital where former Russian acting prime minister Yegor Gaidar was treated after he collapsed at the Co Kildare university last Saturday.
A Health Service Executive (HSE) spokeswoman said the tests were "purely a precautionary measure".
Mr Gaidar, now an influential liberal academic in Russia and critic of Russian President Vladimir Putin, collapsed with what his daughter described as a "mystery illness" while attending a conference at the NUI.
Gardaí launched an investigation yesterday after Mr Gaidar's former colleague, and head of Russia's electricity supplier, Anatoly Chubais, said he believed there was a link between Mr Gaidar's condition, the death of Mr Litvinenko, and the murder of eminent Russian investigative journalist Anna Politkovskya.
Mr Gaidar and Mr Litvinenko are not thought to have met recently but it has been speculated that both were in contact with a mutual associate in recent weeks.
Meanwhile, initial tests on the Italian academic Mario Scaramella who met Mr Litvinenko on the day he fell ill, show no sign of radiation poisoning.
Mr Scaramella was admitted to hospital in London when polonium 210 was detected in his body.
Further tests are due to be carried out over the weekend.