The two nations were conducting military drills

North Korea’s foreign ministry has accused the U.S. of “intentionally” ramping up tensions by flying in joint military drills with South Korea.

It follows Seoul and Washington announcing they will be conducting the exercises between March 13 and 23.

There are also reports Kim Yo-jong, the powerful sister of North Korean leader Kim Jong-un, has warned the nation is ready to take overwhelming action against the activities.

It’s believed the younger Kim issued the warning in a statement carried by the North’s state-run Korean Central News Agency – or the KCNA.

Pyongyang says it’s closely watching the military activities of South Korea and the U.S., and is ready to act at any time.

Kim added allies should refrain from actions that further aggravate the situation.

The warning comes amid the increasingly frequent deployments of U.S. strategic assets to the Korean Peninsula, most recently with an air drill over the Yellow Sea on Monday.