Letters containing box-cutter blades have been sent to two senior Liberal Democratic Party officials, including Secretary General Tsutomu Takebe, police said Friday.
The Metropolitan Police Department said it is investigating the incidents as harassment attempts from a single party.
According to investigations, Takebe's office got a letter Thursday containing a 3-cm blade and a handwritten note from a "Yoshiaki Horie," which was spelled using the same kanji used in the names of financier Yoshiaki Murakami and Livedoor Co. founder Takafumi Horie, who have been indicted on Securities and Exchange Law violations.
Murakami has been charged with insider trading, while Horie stands accused of falsifying earnings reports.
The letter was postmarked in Fukuyama Higashi, a post office in Hiroshima Prefecture.
Meanwhile, the office of Toranosuke Katayama, secretary general of the LDP's House of Councilors caucus, said it also received a letter Thursday. The letter, which came with an 8-cm blade, was typewritten and said: "Offer your life in apology to the Japanese people," investigators said.
According to office staff, the letter was postmarked by the Tomisato Post Office in Chiba Prefecture.
Both offices are located in the Diet complex.