Police have launched a major investigation into online threats of copycat crimes following recent stabbing attacks in and around Seoul.

The National Police Agency has warned it will sternly respond to such threats, which have cropped up nationwide, saying they stoke public fear and anxiety.

The Seoul Police said Saturday that they apprehended three more people suspected of threatening to commit similar crimes, following two earlier arrests, raising the tally thus far to five.

As of 7 a.m. Saturday, at least 42 online threats have been discovered since the stabbing rampage in Bundang, south of Seoul on Thursday. The messages were posted on various platforms including social media and anonymous bulletins for university students.

Those who wrote 13 of the 42 threats have been identified and are currently being questioned. Police are continuing to track down others using IP addresses.

Officers are considering applying charges of blackmail which may carry up to seven years in prison or a ten million won fine. 

Following the stabbing sprees, the police on Friday declared a special crackdown to enhance public security, involving the deployment of 12-thousand officers to over 200 locations nationwide including crowded locales such as department stores and subway stations.