Photo/IllutrationThe Kanda Post Office in Tokyo’s Chiyoda Ward on Jan. 30 (Nobufumi Yamada)

Extortion letters sent to 18 companies across Japan were all mailed from the Kanda district in Tokyo’s Chiyoda Ward, and police confirmed that 14 of them contained deadly potassium cyanide, investigative sources said.

The letters, demanding cryptocurrency payments and threatening distribution of poisonous drugs, had been sent to 18 companies in Tokyo, Osaka and Sapporo as of Jan. 30.

In the capital, the targets were 11 pharmaceutical companies, one food company and two newspaper publishers--The Asahi Shimbun and The Mainichi Shimbun.

The white powder contained in the 14 letters delivered in Tokyo was confirmed as potassium cyanide, the sources said.

In Osaka, the letters were sent to three pharmaceutical companies, while the Sapporo branch of a food company was also targeted.

The sources said all 18 envelopes carried a Kanda postmark with the date of Jan. 24, when they were processed at the Kanda Post Office. Each company apparently received the envelopes on Jan. 25.

According to Japan Post Co., the postmark would appear on letters placed in about 170 mailboxes that fall under the jurisdiction of the Kanda Post Office.

The Metropolitan Police Department has been analyzing the poison distribution route and security camera footage. It is cooperating with police in Osaka and Sapporo in the investigation.

The extortion letters were typed by computer on A-4 paper. They all read: “Drugs laced with potassium cyanide will be distributed. Send Bitcoins worth 35 million won (3.5 million yen, or $32,000) by Feb. 22, or a tragedy will occur.”

A special font was partly used in the letter.