Seoul: North Korea on Friday claimed that it had tested an underwater nuclear attack drone able to unleash a "radioactive tsunami," amid deteriorating relations with the US, reported CNN.

A report from the state-run Korean Central News Agency (KCNA) said the drone, called the "Unmanned Underwater Nuclear Attack Craft 'Haeil,'" was tested from March 21 to 23, cruising in waters off the country's east coast for more than 59 hours before its test warhead was detonated on Thursday afternoon.

"The mission of the underwater nuclear strategic weapon is to stealthily infiltrate into operational waters and make a super-scale radioactive tsunami through underwater explosion to destroy naval striker groups and major operational ports of the enemy," the KCNA report said.

However, analysts questioned North Korea's claims, noting that North Korea has previously exaggerated its capabilities and deployment timelines, reported CNN.

"Pyongyang's latest claim to have a nuclear-capable underwater drone should be met with skepticism" because North Korea offered no proof, said Leif-Eric Easley, associate professor of international studies at Ewha Womans University in Seoul.

In March 2022, North Korea released footage of what it claimed was a new intercontinental ballistic missile (ICBM) that was later discredited by experts.

North Korea's drone test claim comes at the same time Pyongyang said it tested nuclear-capable cruise missiles this week.

Four of the subsonic missiles hit targets in the East Sea, also known as the Sea of Japan, after flying oval and figure-8 patterns of 1,500 and 1,800 kms (932 and 1,118 miles) on Wednesday, KCNA reported.

Wednesday's drill "let strategic cruise missile units get familiar with the procedures and processes for carrying out the tactical nuclear attack missions," the report said.

The KCNA report said Pyongyang's nuclear weapons development was necessary to counter "the reckless military provocations being escalated by the US and the South Korean authorities."

US and South Korean forces have been holding their biggest war games in five years on the southern part of the Korean Peninsula.

North Korea has been testing various missiles at the same time, including the test of an intercontinental ballistic missile last week and the tests of smaller-range missiles like the cruise missiles tested on Wednesday.