Police have raided the National Information Resources Service(NIRS) and other locations as part of an investigation into a recent fire at the state data center.

An investigation team from the Daejeon Police Agency began conducting search and seizure operations at 9 a.m. Thursday at the NIRS and three companies that were involved in the data center's work at the time of the fire.

Around 30 officers are participating in the raids to secure evidence.

Earlier, the police placed four individuals under investigation for professional negligence in connection with the fire: one NIRS employee, two contractors involved in battery relocation and one contracted supervisor.

The fire broke out last Friday on the fifth floor at the NIRS data center in Daejeon, taking down 647 online government systems. 

Only 17 percent of the affected services had been restored as of 6 a.m. on Thursday.