K-pop star Rain is under investigation by prosecutors on charges of violating the military code of conduct during his mandatory service, prosecution officials said Thursday.

The probe comes after an unidentified person had filed a charge against the 30-year-old singer, whose real name is Jung Ji-hoon, for spending too many days off duty before being discharged in July, they said.

All able-bodied South Korean men are required to serve about two years in the armed forces.

Rain spent 21 months as an "entertainment soldier" as part of a special unit designated by the defense ministry as an agency for promotion. The now-defunct entertainment unit had employed actors, singers and other entertainers to provide TV and radio programming geared toward military audiences before it was abolished amid rising criticism over the special treatment the entertainer soldiers received.

"We will not give details as it is an ongoing investigation," said a prosecutor at the Seoul Central District Prosecutors' Office probing the case. "We will call in (Rain) if it is deemed necessary."

Jung faced disciplinary action earlier this year after photographs surfaced showing him on a date with famous actress Kim Tae-hee while on work-related duty.

According to the defense ministry, Rain had spent 71 days off duty in 2012, his first year serving in the unit. The number is much larger than the average 43 days given to an ordinary soldier from 2009 through last year.

Rain is one of the most popular male celebrities in South Korea and a well-known star in other Asian countries, and has appeared in several TV series and films. (Yonhap News)