Nuclear-armed North Korea test-fired two strategic cruise missiles from a submarine on Sunday, state news agency KCNA said on Monday just as US-South Korea military drills were due to begin.

"Strategic" is typically used to describe weapons that have a nuclear capability.

KCNA said the launch confirmed the reliability of the system and tested the underwater offensive operations of submarine units that form part of North Korea's nuclear deterrent.

South Korea's Joint Chiefs of Staff said the military was on high alert and the country's intelligence agency was working with its US counterpart to analyse the specifics of the launch.

On Monday, South Korean and American troops were scheduled to begin 11 days of joint drills, dubbed "Freedom Shield 23," which will be held on a scale not seen since 2017.

The drills will strengthen the allies' combined defensive posture, the two militaries have said, and will feature field exercises including amphibious landings.

North Korea has long bristled over drills they regard as a rehearsal for invasion. It has conducted a record number of missile tests and drills in the past year in what it says is an effort to boost its nuclear deterrent and make more weapons fully operational.

The submarine launches aimed to show North Korea's determination to control a situation in which, KCNA said, "the US imperialists and the south Korean puppet forces are getting evermore undisguised in their anti-DPRK military maneuvers."

DPRK stands for North Korea, officially the Democratic People's Republic of Korea.

(Reuters)

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