Police have booked actor Lee Sun-kyun on charges of illegal drug use.

The Incheon Metropolitan Police said on Monday that they have booked Lee and two others for violating the narcotics law, with an investigation prior to booking ongoing for five others.

Those subject to the ongoing interal probe include Hwang Ha-na, the granddaughter of the late founder of Namyang Dairy Products, a celebrity trainee and an employee of an entertainment venue, some of whom reportedly have a record of drug conviction.

Another employee at the same business who reportedly made repeated contact with Lee since early this year was taken into police custody on the weekend.

Investigators suspect that those under investigation had used illegal drugs at such an establishment in Seoul's Gangnam area and their respective residences.

Police are expected to summon the 48-year-old actor for questioning and take hair and urine samples for drug testing.

Last Friday, Lee's management agency issued a statement apologizing for causing public concern and pledged to faithfully cooperate with the police, while also revealing that the actor had been subject to blackmail threats, prompting him to file a complaint with the prosecution against three people who are now under investigation.

Lee played Dong-ik, the father of the wealthy family in director Bong Joon-ho's Oscar-winning 2019 film "Parasite," taking home a Screen Actors Guild Award for Outstanding Performance by a Cast in a Motion Picture the following year.