The Foreign Ministry reported to authorities on Friday that it had received a suspicious envelope, prompting the Metropolitan Police Department's bomb squad to rush to the ministry in Tokyo, the police said.
The envelope contained a plastic bottle with its lid open, something like a warning flare and a letter. The police are investigating the case as a possible forcible obstruction of business.
The white, A4-size envelope had the phrase "To all the staff members" written on it along with the sender's name and address. It was postmarked at a post office in Aichi Prefecture.
The ministry building in Tokyo's Kasumigaseki district was cordoned off as passers-by watched police officers in protective gear work at the scene.