The National Intelligence Service(NIS) and police raided multiple locations on Wednesday, including the headquarters of the Korean Confederation of Trade Unions(KCTU) in Seoul, as part of an investigation into a violation of the National Security Act.

There was an intense standoff for three hours involving a physical altercation in the process.

The NIS also raided the office of the Korean Health and Medical Workers' Union in Seoul.

The spy agency said it obtained warrants for the raids after securing related evidence in a case they have been working on for years, which is likely related to a National Security Act violation committed by a progressive figure in Jeju.