A threatening message warning of an attack using sulfuric acid to blind Tokyo Gov. Yuriko Koike has been sent to some of those linked to the governor, investigative sources said.

Renho, who is running against Koike in the July 7 Tokyo gubernatorial election, has also received a death threat. Tokyo's Metropolitan Police Department is investigating the incidents as suspected intimidation.

The sources said Monday that a fax message was sent that day to people linked to regional political party Tomin First no Kai, to which Koike serves as special adviser, and the office of a party member in the Toshima Ward Assembly in Tokyo.

The message contained threats such as "I have obtained a high-performance bomb and sulfuric acid," "I will pour sulfuric acid on Yuriko Koike and blind her," and "I will blow up Yuriko Koike's election office, like with Renho."

Some of the recipients have contacted the MPD.

Renho's election office received a fax message Sunday morning threatening to "repeatedly stab Renho to death with a knife" and "set up explosives and detonate them on June 24." The gubernatorial candidate, a former member of the House of Councilors, has filed a police report through an attorney.

Renho left the Constitutional Democratic Party of Japan, the country's largest opposition party, earlier this month to run in the Tokyo gubernatorial election as an independent candidate.

The incidents happened during the official campaigning period for the gubernatorial election, which began last Thursday.