Police have warned that any false reports about explosive devices in public places will be met with intensive investigation and a stern response.

Meeting with the local press on Monday after a recent series of bomb hoaxes, the National Police Agency’s acting Commissioner General Yoo Jae-seong said attempts to intimidate people through such acts will be taken very seriously as threats to public order.

Violators could face up to five years in prison or fines of up to 20 million won, or around 14-thousand U.S. dollars.

After an empty threat was posted online early this month indicating that the poster had planted explosives in a department store in Seoul’s Jung District, similar threats were made against the Jamsil Sports Complex in Seoul, Andong Station in the capital of North Gyeongsang Province, and a fast food chain in Suwon, Gyeonggi Province.

The acting police chief said all but one of those cases have resulted in arrests and that discussion is underway about preventive measures.