South Korea, the United States, Japan are set to hold joint military drills from Monday through Friday off the South's Jeju Island, combining naval, air and missile-defence exercises to better prepare against threats from the nuclear-armed North.

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

Kim Yo Jong 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, which is the wrong place, will inevitably bring bad results to themselves," she said, using the acronym for North Korea.

Pyongyang has long balked at such joint military drills involving the allies, calling them rehearsals for an invasion.

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

Since a failed summit with the United States in 2019 on denuclearisation, North Korea has repeatedly said it will never give up its nuclear weapons and declared itself an "irreversible" nuclear state.

Kim Jong Un has been emboldened by the war in Ukraine, securing critical support from Russia after sending thousands of North Korean troops to fight alongside Moscow.

Moscow and Pyongyang signed a mutual defence pact last year when Russian President Vladimir Putin visited the reclusive state.