Thirty-six employees of a Turkish company that provides ground handling services to British Airways began undergoing precautionary radiation tests, the company said today.

Doctors have failed to diagnose former Russian Prime Minister Yegor Gaidar’s mysterious illness, saying they suspected poisoning, but were unable to detect the toxic substance that could be to blame, an aide said today.

British police investigating the poisoning death of a former KGB agent have officially requested assistance from their Russian counterparts, prosecutors said, as officers arrived in Moscow amid rising diplomatic tensions.