North Korea on Tuesday threatened "merciless retaliation" in response to U.S.-South Korean military drills.

A statement from the North's military vowed to launch "merciless retaliation and unsparing punishment," according to The Associated Press.

"No one can vouch that these huge forces concentrated in South Korea will not go over to an actual war action now that the military tensions have reached an extreme pitch in the Korean peninsula," the statement said, according to the AP.

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"Moreover, high-ranking bosses of the U.S. imperialist aggressor forces flew into South Korea to hold a war confab. Such huddle is increasing the gravity of the situation."

The Ulchi Freedom Guardian exercises, which began on Monday, are staged to train the South for dealing with an attack by the North.

This year's exercises will include about 17,500 U.S. troops, with 3,000 not based on the peninsula. It is a "a computer-simulated defensive exercise designed to enhance readiness, protect the region and maintain stability on the Korean Peninsula,” the Pentagon said in a statement last week.

Tensions between the U.S. and North Korea escalated in recent weeks after it was reported that North Korea has successfully miniaturized a nuclear warhead to mount on a missile.

President Trump promised "fire and fury" if North Korea continues to threaten the U.S. and said U.S. military options were already "locked and loaded."