South Korea police investigating Big Bang Daesung's Seoul building

July 29 (UPI) -- South Korea's national police agency said it is investigating a multimillion-dollar commercial building in Seoul's Gangnam district, following reports Daesung of K-pop band Big Bang allowed illegal businesses to flourish on the premises.

Police chief Min Gab-ryong told reporters on Monday the agency has been "gathering intelligence" on the building owned by Daesung, whose legal name is Kang Dae-sung, Yonhap reported.

Kang, who is serving his mandatory military service, purchased the building for about $26 million in 2017, according to local television network Channel A.

The network was the first to break the story of illegal operations at the building late last week.

The news service sent a television crew to investigate the building, and discovered a subterranean floor and floors 5 through 8 were off-limits to the public, with non-functioning elevator buttons for some of the floors.

The floors are also officially registered as "offices" and "restaurants," according to Channel A's report.

Television footage from Thursday shows a reporter trying to access the eighth floor of Kang's building during daytime, but the elevator opens to stainless steel shutters.

At night, the building "came to life," with lights coming on the restricted floors and young women arriving in "luxury vehicles," according to Channel A.

Sources who spoke to the network said the subterranean floor is a "strange place" where sex trafficking is taking place.

The television station's undercover reporters were also seen being denied entry in secretly recorded footage; an employee tells them they "don't receive new guests."

Other sources said guests would leave for a nearby motel.

On Monday the national police agency would not confirm whether illicit sex trade took place at the site, but confirmed the building's tenants have been found guilty of violating food sanitation laws.

Big Bang was in the spotlight earlier this year when police arrested thousands following drugging and rape incidents at Burning Sun, a nightclub owned by Big Bang band member Seungri.