North Korea has decided to expel US soldier Travis King, who was detained after crossing the border from the South in July, the KCNA state news agency said on Wednesday.

After completing its investigation, the "relevant organ of the DPRK decided to expel Travis King, a soldier of the U.S. Army who illegally intruded into the territory of the DPRK, under the law of the Republic", KCNA said, using the North's formal name.

It did not give any details about where or when King would be released.

North Korea claims King defected to escape mistreatment and racial discrimination in the US Army.

"According to the investigation by a relevant organ of the DPRK, Travis King confessed that he illegally intruded into the territory of the DPRK as he harboured ill feeling against inhuman maltreatment and racial discrimination within the U.S. army and was disillusioned about the unequal U.S. society," the report said.

King ran across the border on July 18 after joining a sightseeing tour of the Demilitarised Zone between the two Koreas.

The soldier was due to return to the United States to face disciplinary consequences after a drunken bar brawl, an altercation with police and a stint in a South Korean jail. 

But instead, he left the airport, joined a tour of the border and fled across it.

King's border crossing came with relations between the two Koreas at one of their lowest points ever, with diplomacy stalled and North Korean leader Kim Jong Un calling for increased weapons development, including tactical nuclear warheads.