SEOUL, Oct. 19 (Yonhap) -- About 40 people, including public officials and soldiers, are under police investigation on suspicion of producing or circulating pro-North Korean materials on the Internet in breach of the National Security Law, police said Wednesday.

The people under probe are suspected of making or posting materials that extol or propagandize the virtues of the communist country on an extremist pro-North website or their personal Internet homepages, the National Police Agency said.

The suspects include a local pilot with leading airline Korean Air, who is accused of uploading pro-North Korean materials on his own website disguised as a regular scientific research site.

The 44-year-old plane captain surnamed Kim posted about 60 articles or video clips that sympathize with the communist regime on his website, the police said. He was also a member of the extremist pro-North Web community, whose operations are now being suspended.

Kim has been barred from leaving the country following the launch of the investigation. His airline, after being notified of the probe, suspended him from flying on fear that he would fly northward to defect to the communist country, the police noted.

Kim's posting of pro-North content, some of which was produced in the North, goes against the anti-North Korea law that prohibits issuing or possessing such materials, the police also noted.

Police said they searched Kim's home on Tuesday and confiscated around 10 North Korean books and his computer, which had pro-North materials on it. After examining them, police said they plan to call him in for interrogation.

"A further probe will be focused on discovering whether he led active pro-North activities, including personal contact with (pro-North campaign) related people offline," a police official said.

The police agency also said a first lieutenant from the Korean Air Force and several government employees were also included in the group of suspects, alongside a lawyer and a private tutor.

The latest police actions come amid the country's intensifying efforts to step up crackdowns on pro-North Korean activities in cyberspace, which officials worry have mushroomed to a risky level.

Police apprehended a total of 358 perpetrators of anti-state crimes in the past four years, 119 of whom committed pro-North activities in cyberspace, according to the police.

The country regulates Internet content that extols or propagandizes the North Korean leader or the political system of North Korea, which is by law defined as a national enemy since the 1950-53 Korean War ended in an armistice rather than a peace treaty.