Kim Yo Jong, the powerful sister of North Korean leader Kim Jong Un, warned joint military exercises of the United States, South Korea, and Japan could bring about "negative consequences" for themselves, state media reported on Sunday.

South Korea, Japan, and the U.S. will conduct annual defensive drills called the "Freedom Edge" starting on Sept. 15 to upgrade aerial, naval, and cyber operational capabilities against North Korea's nuclear and missile threats, South Korea's military has said.

"This reminds us that the reckless display of power displayed by the U.S., Japan, and South Korea in the wrong places, namely around the Democratic People's Republic of Korea, will undoubtedly bring about negative consequences for themselves," Kim said via state KCNA news agency, using North Korea's official name.

South Korea and the United States also plan to stage the Iron Mace tabletop exercises next week on integrating their conventional and nuclear capabilities against North Korea's threats, South Korean media reported.

If "hostile forces" continue to boast about their power through those joint drills, North Korea will take countermeasures "more clearly and strongly," North Korea's top party official Pak Jong Chon said in a separate dispatch via KCNA.

Pyongyang has traditionally criticized those joint drills as rehearsals for invasion and in some cases responded with weapons tests, but Seoul and Washington say they are purely defensive.