A man close to the chief of an Education Ministry foundation is being questioned in connection with the mailing of radioactive material to 10 government offices last week, police sources said Wednesday.

Investigators suspect the man, a broker acquainted with the 84-year-old director of the foundation, was involved in the director’s storage and sale of more than 10 tons of monazite, a radioactive substance. The man had recently argued with the director over money.

The director of the foundation, based in Tokyo’s Taito Ward, has admitted storing monazite in locations in eastern Japan, including Kumagaya, Saitama Prefecture, and Tatsuno, Nagano Prefecture, the sources said. He told Kyodo News that he imported the substance 20 years ago when he was running a trading company.

Police and Science and Technology Agency officials have already located the stored monazite, but no harmful levels of radioactivity were detected at the two sites.

Envelopes bearing Tokyo postmarks and containing monazite powder were mailed to the 10 government offices, including the Prime Minister’s Official Residence, between June 6 and June 8.

Each envelope contained several grams of the substance, with radioactivity estimated to be less than 1 microsievert, according to police. Such levels are not harmful to humans, they said.

Sources close to the case said that the director’s acquaintance knew about the storage and sale of monazite, and police believe he has information on the incident.

The acquaintance’s name appeared in a message included in the envelopes sent to government offices. The message claimed that the man was smuggling uranium to North Korea for production of nuclear missiles, police sources said.

“Please look into the matter. The material is being shipped to North Korea from a Niigata port. The amount is 70 tons,” the message said, according to the police sources.

Police suspect the director and the broker have violated a law regulating nuclear reactors and nuclear-related facilities, the police sources said.

Monazite is a phosphate containing thorium, which can be used as a nuclear fuel.