Four people in Germany may have ingested the radioactive substance that killed former Russian spy Alexander Litvinenko, German police said, as investigators probed the activities of one of his business associates in Hamburg.

The ex-wife and two children of Dmitry Kovtun, who is being investigated for suspected handling of polonium 210, likely had contact with the substance while Kovtun was in Hamburg in late October, police said at a briefing broadcast on the N24 television channel. A fourth person, Kovtun's ex-wife's partner, also tested positive.

German authorities discovered radioactive traces linked to Kovtun that he left while visiting the city days before his Nov. 1 meeting with Litvinenko, who died last month in London following radiation poisoning. The probe expands a case involving former agents.