SEOUL - North Korea tested two strategic cruise missiles from a submarine on Sunday, according to the state news agency KCNA, just as US-South Korean military drills were set to begin.

The term "strategic" is commonly used to describe nuclear-capable weapons.

The launch, according to KCNA, confirmed the system's dependability and tested the underwater offensive operations of the submarine units that comprise North Korea's nuclear deterrent.

South Korea's Joint Chiefs of Staff (JCS) said the military was on high alert, and the country's intelligence agency was analyzing the details of the launch with its US counterpart.

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

According to the two militaries, the drills will strengthen the allies' combined defensive posture and include field exercises such as amphibious landings.

North Korea has long objected to drills that it sees as a dress rehearsal for an invasion. It has conducted a record number of missile tests and drills in the last year in an effort to boost its nuclear deterrent and make more weapons fully operational, according to the Pentagon.

"It's miserable that North Korea is using our regular, defensive drills as a pretext for provocation," said Koo Byoung-sam, a spokesman for South Korea's unification ministry, which handles relations with the North. "I hope North Korea realizes that escalating tensions on the Korean peninsula will earn them nothing."

The submarine launches were intended to demonstrate North Korea's determination to maintain control of a situation in which, according to KCNA, "the US imperialists and South Korean puppet forces are becoming ever more undisguised in their anti-DPRK military manoeuvres."

The acronym DPRK stands for North Korea, which is officially known as the Democratic People's Republic of Korea.

According to KCNA, the strategic cruise missiles were launched from the "8.24 Yongung" submarine in the early hours of Sunday off the east coast of Korea.

According to the KCNA report, the missiles traveled approximately 1,500 kilometers (932 miles) before striking a target in the sea.

A JCS spokesperson stated that not everything North Korea claimed was true, but he did not elaborate.

Hirokazu Matsuno, Japan's Chief Cabinet Secretary, stated that there was no evidence that the missile flew into Japanese waters or caused any damage.

"We are concerned if North Korea's claim that the missile has a range of more than 1,500 kilometers is true," Matsuno said.

He stated that US military deterrence in the Asia-Pacific region is "essential," adding that the North "may step onto further provocative acts such as a nuclear test."

North Korea, according to Leif-Eric Easley, a professor at Ewha University in Seoul, may be exaggerating its ability to arm such missiles with nuclear warheads.

"The Kim regime wishes to demonstrate that it can match or outperform military capabilities on display during US-South Korean defense exercises. However, North Korean soldiers are undernourished and have been ordered to assist farmers in addressing the country's food shortage "Easley stated.

North Korea has a large submarine fleet, but the only known experimental ballistic missile submarine is the 8.24 Yongung (August 24th Hero). According to analysts, it is critical in the development of missiles, submarine technology, and operational procedures, as well as the hands-on training of new submariners.

According to North Korea, a functioning ballistic missile submarine is being built.

Kim Jong Un, the leader of North Korea, gave instructions to the military to step up training exercises to prevent and, if necessary, respond to a "real war" while supervising the launch of a short-range ballistic missile (SRBM) exercise on Thursday.

Kim oversaw a ruling party meeting on Sunday, according to state media, where "important, practical measures" to strengthen the nation's war deterrence in the face of stepped-up actions by the United States and South Korea were discussed and decided. The measures were not described in detail in the report.