North Korea claimed on Friday morning that it tested a "nuclear underwater attack drone" this week amid joint U.S. and South Korean military drills, according to state media outlet Korean Central News Agency. 

The new underwater weapon is designed to "stealthily infiltrate into operational waters" and target naval striker groups and enemy ports, North Korea claimed. 

"This nuclear underwater attack drone can be deployed at any coast and port or towed by a surface ship for operation," KCNA said in a statement. A test warhead exploded in the waters off Hongwon Bay on Thursday afternoon, North Korea claimed. 

The weapons test came as the U.S. and South Korea wrapped up Freedom Shield 23, a series of military drills around the Korean Peninsula that began on March 11. The U.S., India, Japan, Canada and South Korea also began Sea Dragon 23 last week, an anti-submarine warfare exercise in the Indo-Pacific region. 

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North Korea lashed out at the "U.S. imperialists and the South Korean puppet regime of traitors" for the exercises, saying that the political situation on the Korean Peninsula is at "an irreversibly dangerous point."

"The hostile forces' anti-DPRK war scenario based on the deployment of huge nuclear strategic assets, the amount of forces involved in carrying it out and the ensuing peculiar mode of war urgently require the DPRK to make its entire armed forces gird themselves for an all-out war," Pyongyang's state media said. 

North Korea also fired multiple strategic cruise missiles from the South Hamgyong province on Wednesday. 

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Chairman of the Joint Chiefs of Staff U.S. Army Gen. Mark Milley testified before Congress on Thursday that China remains the U.S.'s "number one long-term geostrategic security challenge," but noted that North Korea is also a major threat in the region. 

"North Korea’s continued ballistic missile testing and nuclear weapons development pose real threats to our homeland as well as allies and partners in the Indo-Pacific," Milley told the House Appropriations Committee.