TOKYO • Nine Japanese companies, including drugmakers and a newspaper publisher, have received blackmail letters containing white powder suspected to be cyanide, police and local media said yesterday.

The letters were sent under the names of executed members of the Aum Shinrikyo - the Japanese doomsday cult behind the deadly 1995 sarin gas attack in Tokyo - and demanded 35 million won (S$42,350) in bitcoins, a police spokesman told Agence France-Presse.

"Major pharmaceutical and other companies... received envelopes with threatening letters and a powdery substance" suspected to be cyanide, he said, without identifying the companies.

According to the spokesman, the letter said: "I will make fake medicine containing potassium cyanide and distribute it," and warned "a tragedy will happen" if the money was not transferred by Feb 22.

Local media said the names on the letters - which were received on Friday - included Shoko Asahara, the charismatic leader of the sect, who was executed with 12 of his one-time followers in July last year.

The white powdery substance was later confirmed to be cyanide, the Asahi Shimbun newspaper reported, adding that a similar envelope was also sent to the Tokyo headquarters of the Mainichi Shimbun newspaper.

A pharmaceutical firm in Osaka and the Hokkaido branch of a Tokyo-based food company also received letters the same day, Kyodo News reported, though the police declined to name the companies.

Similar threatening letters were sent to some pharmaceutical companies in Osaka in January last year, Jiji Press reported.

The letters also carried different addresses, such as detention facilities in Tokyo, Kyodo News reported.