North Korea threatened to unleash a powerful action if the U.S. does not halt joint military drills with partners including South Korea, in what might be an effort by Kim Jong Un to lay the ground for his first nuclear test in five years.

"If the U.S. continuously persists in the grave military provocations, the DPRK will take into account more powerful follow-up measures,” the state’s Foreign Ministry said in a statement released on official media Tuesday. Such ministry statements are often used by the country, officially known as the Democratic People’s Republic of Korea, to make clear the warning is coming from Kim’s regime.

The U.S. and South Korea this week started joint air drills known as Vigilant Storm that will run through Friday and involve about 240 aircraft in about 1,600 sorties to "hone their wartime capabilities,” the U.S. 7th Air Force said in a statement.