British authorities planned to contact thousands of British Airways passengers on Wednesday after traces of radiation were found on at least two jetliners during the investigation into the poisoning death of a former Russian spy.

Two planes at London's Heathrow Airport tested positive for traces of radiation and a third plane has been taken out of service in Moscow awaiting examination, British Airways said in a statement.

High doses of polonium-210 — usually manufactured in specialized nuclear facilities — were found in Alexander Litvinenko's body after he died last week in London. Traces of radiation have been found at sites in London connected with the investigation of his death.

The airline said it was contacted by the British government late Tuesday and told to ground the planes for investigators looking into the death of the former intelligence agent to test them for radiation.

All three planes had been on the London-Moscow route, British Airways said. In the last three weeks, the planes had also travelled to routes across Europe, including Barcelona, Frankfurt and Athens.

Around 30,000 passengers had travelled on 220 flights on those planes, said Kate Gay, a spokeswoman for the airline.

"The airline is in the process of making contact with customers who have travelled on flights operated by these aircraft, which operate within Europe," British Airways said in a statement, adding the risk to the public was low.

The airline has published the flights affected on its website and told customers on these flights to contact a special help-line set up by the Health Ministry.

Freelance reporter Christopher Lee told CBC News from London that about 1,200 people have called the help-line in the city alone.

Home Secretary John Reid disclosed the searches following a meeting with COBRA, the government's top-level emergency planning committee. Reid said experts had tested two planes so far and planned to check a third.

British Airways said the investigation was confined to the three planes, which would remain out of service until further notice.

Implicated Putin in his murder

The ex-spy fell ill in early November and told police he believed he was poisoned on Nov. 1 while dining at a sushi bar, where he met a contact during his investigation into the slaying of Russian journalist Anna Politkovskaya.

Like Litvinenko, the murdered reporter had been critical of Russian President Vladimir Putin's government.

Within three weeks, Litvinenko's hair fell out, his throat became swollen, and his immune and nervous systems suffered severe damage.

He died accusing Putin of orchestrating his murder, but London police are still investigating it as a "suspicious death" and have not ruled out the possibility Litvinenko may have poisoned himself.

With files from the Associated Press