Kim Yo Jong, the powerful sister of North Korean leader Kim Jong Un, condemned upcoming joint military drills by South Korea, the United States and Japan as a "reckless show of strength" that would bring "bad results", state media said on Sunday.

The allies are set to hold joint military drills from Monday through Friday off the South's Jeju Island.

Seoul and Washington, which stations around 28,500 troops in South Korea, will also stage a tabletop military exercise, aimed at integrating their military assets.

Kim slammed the drills as a "dangerous idea", in a statement carried by state news outlet KCNA.

"The reckless show of strength made by them (the allies) in real action in the vicinity of the DPRK (Democratic People's Republic of Korea), which is the wrong place, will inevitably bring bad results to themselves," she said.

Pyongyang has long baulked at such joint military drills, calling them rehearsals for an invasion.

Kim Jo Yong's statement follows a recent visit by her brother to weapons research facilities, where he said Pyongyang "would put forward the policy of simultaneously pushing forward the building of nuclear forces and conventional armed forces". (AFP)