"Traces of contamination have been discovered at two places in the flat where (Kovtun's) former wife lived," a police statement said. It said the 31-year-old woman was being questioned by police.

Traces of radioactivity were also found at the home of Kovtun's former mother-in-law in the town of Haselau, west of Hamburg, police said. But no radioactivity was detected at another flat in the building where Kovtun himself had lived, the statement said.

Police experts were trying to determine if the radioactivity came from the substance polonium 21.

Investigators believe Kovtun could have been in contact with the highly radioactive substance which killed Litvinenko on Nov. 23.

Kovtun fallen ill

Kovtun, a 41-year-old businessman, recently told Moscow Echo radio station that he had lived in Germany for 12 years and had been married to a German woman.

Police denied German press reports that they suspect Litvinenko's murder may have been planned by Kovtun in Hamburg.

"At the moment, this man (Kovtun) has not been accused," said a police spokeswoman in Hamburg, Ulrike Sweden.

Kovtun, one of three Russians who met Litvinenko in London on Nov. 1, shortly before the former intelligence agent fell ill, was reported Friday to be suffering from radiation sickness.

Russia's Interfax news agency quoted an unnamed medical official in Moscow as saying that Kovtun had briefly fallen into a coma Thursday but had since recovered consciousness.

The death of Litvinenko from polonium poisoning, which British authorities are treating as murder, has prompted a media outcry, heightened by allegations from the dead agent's friends that he was killed on the orders of Russian President Vladimir Putin.

Hamburg hotline for concerned public

The Hamburg apartment building, where about 30 people live, was evacuated while the police searched the two flats. But police said the radioactivity poses no danger to the residents. Polonium 210 is only dangerous if it is ingested or comes into contact with open wounds, they said.

Hamburg police appealed to "people who had any contact" with Kovtun to come forward. Concerned members of the public in Germany can call 040 - 42 67 65.