In response to the start of a joint U.S.-South Korean military drill, North Korea threatened to launch a “preemptive nuclear strike” against South Korea and the U.S., according to reports.

The Ulchi Freedom Guardian exercise, an annual military drill, began Monday. The drill will last for two weeks and will include 75,000 troops, 25,000 of whom are American, reports the Yonhap News Agency.

Just as it has done for past drills, the U.N. Command Military Armistice Commission reportedly informed the North Korean military that the ongoing drills are training exercises and are “non-provocative.” North Korea, however, claims that the U.S.-South Korean joint exercises are clear preparations for a full-scale invasion of its territory.

“From now on, the Korean People’s Army’s (KPA) combined units for primary strike are constantly on high alert to deal a preemptive counterstrike to all the enemy’s offensive groups involved in the drill,” a KPA spokesperson told the Korean Central News Agency (KPCA) earlier today.

“The nuclear war maniacs should keep in mind that the KPA would mount a merciless preemptive nuclear strike of Korean style to the source of provocation to reduce it to rubbles if they show any slight sign of aggression against the DPRK’s territory, water and airspace,” the KPA spokesperson added.

North Korea’s outrage over a standard military exercise belies Kim Jong Un’s anxiety over “cracks” in the foundation of the authoritarian regime following a recent string of major defections.

South Korea announced Wednesday that Thae Yong-ho, a North Korean diplomat in the DPRK’s London embassy, defected. This is the highest-level official to defect in two decades, reports The New York Times. In response to this defection, North Korea called Thae “human scum” who ran to escape punishments for criminal activities.

South Korea is aware of the DPRK’s fragile state. “Recently, even North Korea’s elite group is collapsing, followed by key figures defecting to foreign countries, showing a sign of serious cracks,” explained South Korean President Park Guen-hye at a National Security Council meeting on Monday.

Fearing the collapse of the North Korean regime and increases in America’s military presence near its borders, China has joined its little brother to the north in criticizing U.S.-ROK joint military exercises.

The Xinhua News Agency, China’s state-run media outlet, argues, “The large-scale joint military drills conducted by South Korea and the United States will jeopardize peace and stability in Northeast Asia, especially after tensions have escalated by the planned deployment of a U.S. missile defense system in South Korea.”

China’s Xinhua added, “Although Seoul and Washington claimed that their drills are defensive, the exercises that simulate an all-out-attack by the Democratic People’s Republic of Korea (DPRK) will make Pyongyang more aggressive and will worsen the already fragile and unstable situation on the Korean peninsula.”

The U.S.-South Korean drills will conclude September 2.

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