North Korea claimed Friday to have tested an underwater attack drone capable of unleashing a "super-scale radioactive tsunami" if armed with a nuclear warhead. The brazen claim — which many experts doubt  — was part of the Kim Jong Un regime's angry response to the latest joint war games by the U.S. and South Korean militaries.

The North released pictures of Kim admiring what the country's official news service said was the new underwater drone, and others purportedly showing it at sea, along with an underwater explosion. The regime claimed the weapon cruised underwater for almost 60 hours before blowing up.

North Korea claimed the device, if armed with a nuclear warhead, was designed to "stealthily infiltrate into operational waters and make a super-scale radioactive tsunami through an underwater explosion" to wipe out an enemy naval strike group or port, according to its state media.

• North Korea says latest missile test was nuclear counterstrike simulation  

The North's official Korean Central News Agency said the new weapon could be launched from the shore or towed and then released by a ship.

Kim also observed conventional weapons tests as part of three-day drills meant to send a message to the U.S. and South Korea after their own exercises. North Korea has test fired cruise missiles at targets in the ocean and launched a missile from a submarine over the past two weeks — all of which the regime claims are capable of carrying nuclear warheads.

Military analysts are skeptical, however, that the country has the technology required to fit its nuclear warheads to the more advanced, long-range weapons in its arsenal — at least for now. The North has demonstrated the ability to reach the U.S. mainland with its larger intercontinental ballistic missiles, for instance, but it has not shown the capacity to make a nuclear warhead capable of fitting onto one of the weapons.

The North's state-run media suggested the country had been developing the underwater attack drone since 2012 and tested it more than 50 times over the past couple years, according to The Associated Press, but the weapon has never been mentioned previously.

Kim Dong-yub, a professor at Seoul's University of North Korean Studies, told the AP that the North's claims about the drone couldn't be verified, but the test was likely aimed at demonstrating the weapon could reach South Korea's ports, more than its purported nuclear capabilities.

Ankit Panda, at the Carnegie Endowment for International Peace, told the AP that it would be illogical for North Korea to devote resources to such a weapon for the delivery of nuclear warheads when it has limited amounts of nuclear materials, and it already has ballistic missiles that can likely already carry such warheads greater distances.  

Panda told the AP the drone system would "be vulnerable to anti-submarine warfare capabilities if it were to deploy beyond North Korea's coastal waters," as well as to pre-emptive strikes in port before deployment.

This week's intense display of weaponry by Kim's military was a direct response to the major, 11-day joint U.S.-South Korean exercise dubbed "Freedom Shield," which wrapped up Thursday. It was the biggest joint exercise by the close allies in five years, and it included live fire tank maneuvers and an amphibious landing.

North Korea denounced the exercises, which it called a rehearsal for an invasion. As the drills concluded, South Korea said it was preparing with the U.S. for another round of joint naval exercises. The AP said there were reports in South Korea that the next war games would involve an American aircraft carrier group, but the U.S. military has not confirmed the plans.

North Korea's KCNA said the country's latest weapons tests were intended to put the U.S. and South Korea on alert that the risk of a "nuclear crisis" was increasing as amid the allies' "intentional, persistent and provocative war drills."

In:
• Kim Jong Un
• War
• South Korea
• Nuclear Weapons
• Nuclear Attack
• Drone
• North Korea

Elizabeth Palmer

Elizabeth Palmer has been a CBS News correspondent since August 2000. She has been based in London since late 2003, after having been based in Moscow (2000-03). Palmer reports primarily for the "CBS Evening News."