North Korea on Tuesday sent back a South Korean man it held for about six weeks for entering the country illegally, South Korean officials said.

The 48-year-old, who was sent by the North through the border village of Panmunjom, is currently being investigated by South Korean officials over why he entered the North without government permission, said an official from Seoul's Unification Ministry, who didn't want to be named, citing office rules.

The man, identified only by his surname Lee, was detained by North Korean officials on Sept. 30 after entering the North from China.

The ministry official said the North did not elaborate on the circumstances of Lee's entry and said it was releasing him as a humanitarian gesture.

South Koreans who cross into the impoverished, totalitarian North Korea for the purpose of defecting are rare. The North often repatriates such individuals, although it holds longer detainees it accuses of more serious crimes such as spying to try to win political concessions.

North Korea last month freed Won Moon Joo, a South Korean national who is a student for New York University, six months after he had been arrested for crossing the border from China into North Korea. The release of Joo, whose alleged crime was relatively minor, was seen by analysts as a sign that Pyongyang was trying to improve its ties with Seoul.

North Korea is currently detaining at least three South Korean citizens, including two who in June were sentenced to life in prison with labor after the North's Supreme Court found them guilty of spying for Seoul. North Korea has been holding another South Korean man since late 2013 for allegedly spying and trying to set up underground churches in the North.