North Korea said Friday it tested earlier this week a new underwater nuclear attack drone it claims can generate radioactive tsunami to destroy enemy ships and ports, according to state-run media.

Pyongyang also said it test-fired Wednesday four cruise missiles of two different types, with leader Kim Jong Un, who guided the military activities, warning South Korea and the United States that they should stop "reckless" anti-North Korea war drills, the official Korean Central News Agency said.

Undated photo carried March 24, 2023, by the official Rodong Sinmun newspaper shows a test of an underwater nuclear attack drone conducted by North Korea from March 21 to 23. (Photo courtesy of Korea Media)(Kyodo)

Seoul and Washington jointly held the 11-day Freedom Shield exercise through Thursday, the first large-scale springtime military drill in five years.

The new underwater nuclear attack craft named "Haeil," meaning tsunami, was reportedly deployed Tuesday for a drill off the coast of South Hamgyong Province, in the eastern part of North Korea.

KCNA said the drone cruised along an oval and figure-eight course at a depth of 80 to 150 meters in the Sea of Japan for 59 hours and 12 minutes before reaching the target point in the waters off Hongwon Bay which was set as a mock enemy port. A test warhead detonated underwater on Thursday afternoon.

Over the past two years, the secret weapon underwent more than 50 shakedowns, the report claimed.

The test of the cruise missiles tipped with mock nuclear warheads was conducted in Hamhung, South Hamgyong Province, the state-affiliated agency said. It was detected by the South Korean military.

The two "Hwasal-1" strategic cruise missiles and the two "Hwasal-2" missiles accurately hit their target set in the Sea of Japan after flying on programmed oval and figure-eight paths of 1,500 to 1,800 kilometers for about 2 hours and 5 minutes and two and a half hours, respectively, KCNA said.

The tests of the underwater drone and the cruise missiles had no negative impact on the security of the neighboring countries and Kim was "greatly satisfied with the results," it added.

The leader expressed his will to make the United States and South Korea "plunge into despair" through the high-profile demonstration of the powerful war deterrence, the report said.

A cruise missile is fired March 22, 2023 in South Hamgyong Province, eastern North Korea. (KNS/Kyodo)