The powerful sister of North Korea’s leader issued a fresh warning to the U.S. and South Korea, threatening them with severe consequences if they went ahead with joint military drills set to start next week.

Kim Yo Jong said North Korea is monitoring the "restless military moves by the U.S. forces” and its South Korean "puppet military,” adding Pyongyang is "on standby to take appropriate, quick and overwhelming action at any time according to our judgment,” the official Korean Central News Agency reported Tuesday.

The latest comments indicate North Korea could ramp up provocations in conjunction with the drills, with Kim last month threatening to turn the Pacific Ocean into a "firing range” if they went ahead.