North Korea has conducted a test of its underwater nuclear weapons system in a protest against this week’s joint military drills by South Korea, the US and Japan, state media KCNA says.

The test on Friday of the Haeil-5-23 system, a name North Korea has given to its nuclear-capable underwater attack drones, was carried out by the defence ministry’s think tank in the waters off its east coast, the report said, without specifying a date.

“Our army’s underwater nuke-based countering posture is being further rounded off and its various maritime and underwater responsive actions will continue to deter the hostile military manoeuvres of the navies of the US and its allies,” an unnamed spokesman of the ministry said in a statement, according to KCNA.

The navies of South Korea, the US and Japan staged this week three-day joint drills until Wednesday, alongside the US aircraft carrier Carl Vinson, as part of efforts to improve their responses to nuclear-armed North Korea’s threats.

-AAP