An anonymous memo was found Tuesday claiming that a bomb had been planted at Hongdae subway station, but after a search, police found no evidence of an explosive device.

Police said subway officials received a report around 5:05 a.m. of a note found in a men's bathroom in the station, saying, "I'll install a bomb. You'll suffer." Police blocked off the station bathroom area, where they conducted a search until 7 a.m.

Station functions were maintained during the search.

South Korea has recently suffered from a spate of anonymous threats of violence targeting the general public.

Last month, a 32-year-old man was sentenced to one year and six months in prison for posting online threats of bomb threats at six international airports across the country.