A probe into the death of ex-Russian spy Alexander Litvinenko opened on Thursday as tens of thousands of British Airways (BA) passengers were caught up in the investigation of radioactive substances on two planes in the British capital.

Litvinenko, an ex-KGB man, died last week of radiation poisoning.

Traces of the same radiation substance were found on two BA planes on Wednesday.

The probe started at St. Pancras Coroner's Court in London on Thursday morning but will be adjourned until the police investigation has been concluded, Sky news reported.

BA warned an estimated 33,000 passengers and 3,000 staff on Wednesday night that "low levels of radioactive traces" had been found on two of its aircraft at Heathrow airport.

Experts plan to examine a third aircraft in Moscow, the airline said.

A BA spokesman said the planes were being examined because "individuals involved in the Litvinenko case" had traveled on them.

The alert involves 221 flights within Europe made by the three short haul 767s.

In a statement, the BA said it has been advised that "this investigation is confined solely to these three Boeing 767 aircraft, which will remain out of service until further notice."

Source: Xinhua