SEOUL: North Korea launched at least three short-range ballistic missiles (SRBMs) into the East Sea on Wednesday, one of which flew across its de facto maritime border with South Korea for the first time since the end of the 1950-53 Korean War, according to the South's military.

The Joint Chiefs of Staff (JCS) said the missile firing from a site in or around the North's eastern coastal city of Wonsan was detected at around 8:51 a.m, reported Yonhap news agency.

The North's latest provocation came in apparent protest of the five-day large-scale combined air drills of South Korea and the United States that kicked off Monday.

One of the three SRBMs fell into high seas 26 kilometers south of the Northern Limit Line (NLL), an area 57 km east of the South's eastern city of Sokcho and 167 km northwest of Ulleung Island near Dokdo. It headed toward the island before falling into the international sea, prompting local authorities to issue an air raid alert.

The North also fired various types of several other missiles westward and eastward, the JCS said.

"Our military can never tolerate North Korea's provocative act and will sternly respond to it in close cooperation with the US," it said in a statement.

It criticised the North's first firing of a ballistic missile near the South's territorial waters since the division as an "intolerable" act.

It came as Seoul and Washington are staging the Vigilant Storm exercise involving more than 240 aircraft, including their advanced stealth jets, across the skies of the peninsula in a bid to bolster the deterrence posture against the North's threats.

USS Key West, a US nuclear-powered submarine, also arrived in South Korea on Monday for a "scheduled visit" as part of its deployment to the Indo-Pacific region.

The North has long denounced joint military drills between Seoul and Washington as a rehearsal for invasion. The allies stress that the exercises are defensive in nature.

Earlier in the day, Pak Jong-chon, secretary of the Central Committee of the North's ruling Workers' Party, warned that South Korea and the US will pay a "terrible" price if they decide to attack the North.

The North's foreign ministry also threatened the US on Tuesday to carry out "more powerful follow-up measures" if it continues "ceaseless and reckless" military provocations.

-- BERNAMA