The building of Seoul Metropolitan Police Agency / Yonhap

Police are tracking down the writer behind a Japanese-language fax threatening to blow up all middle schools in Seoul, officials said Thursday, prompting schools to beef up security over the threat.

The Seoul Metropolitan Police Agency said it received a report of the fax from an immigration office affiliated with the justice ministry on Wednesday afternoon.

The fax, written in Japanese, claimed it had "already installed" bombs in all middle schools in Seoul and the bomb would go off at 4:33 p.m. Friday.

Authorities believe the case is similar to previous email and fax threats targeting major institutions, which have continued since August 2023.

Police are investigating 38 cases involving similar threats sent by a person claiming to be a Japanese lawyer.

The Seoul Metropolitan Office of Education held an emergency response meeting and informed the relevant schools of the threat.

It also advised each school to toughen entry into the school by outside visitors and strengthen patrols around the school area. (Yonhap)