People watch a TV report on North Korea's launch of an intercontinental ballistic missile (ICBM) toward the East Sea at Seoul Station on July 12, 2023. (Yonhap)

North Korea fired two ballistic missiles toward the waters off its east coast late Monday night in apparent protest against the arrival of a US Navy nuclear-powered submarine in South Korea.

The two short-range ballistic missiles were launched from near the capital city of Pyongyang on Monday between 11:55 p.m. and midnight, South Korea's Joint Chiefs of Staff said.

The military has been analyzing the intentions behind North Korea's late-night missile firings, which mark the third set of launches in less than a week.

On July 19, North Korea fired two short-range ballistic missiles from its capital of Pyongyang toward the East Sea from 3:30 to 3:46 a.m. The missiles flew around 550 kilometers, reaching a distance equal to that of Pyongyang to the Busan port where the Ohio-class USS Kentucky was docked at that time.

Additionally, North Korea fired several cruise missiles toward its west coast at around 4:00 a.m. Saturday.

North Korean state media has been inconsistent with reports of the missile launches, sometimes choosing not to report on the launches at all, sometimes reporting multiple missile launches at once as joint military exercises aimed at both South Korea and the United States.

"Detailed specifications of the missiles and additional activities (by North Korea) are being analyzed by the South Korean and US intelligence authorities," the JCS said, adding that the missiles traveled approximately 400 kilometers before coming down in the East Sea.

"Our military will monitor developments in preparation for further provocations by North Korea in close cooperation with the US," the JCS said.

The missile launch occurred less than one day after the arrival of the Los Angeles-class fast attack submarine the USS Annapolis at the South Korean naval base on Jeju Island on Monday morning.

The South Korean Navy explained that the port visit mainly aims to replenish military supplies during an operational mission. But the South Korean and US Navies have also been discussing staging combined military exercises, such as an anti-submarine warfare exercise, during the visit by the US submarine, a military official who wished to remain anonymous told The Korea Herald.

The dispatch of the USS Annapolis to the peninsula came only three days after the US Navy’s Ohio-class USS Kentucky made a four-day port visit to Busan that ended on Friday. It is the first deployment of a US submarine capable of launching ballistic missiles with nuclear warheads in Korea since the early 1980s.

The recent spate of missile launches comes in the run-up to the 70th anniversary of the 1953 Armistice Agreement that ended the 1950-53 Korean War. North Korea celebrates July 27 as the "Day of Victory in the Great Fatherland Liberation War."

North Korea is widely expected to hold a large-scale military parade to commemorate the day, and it will also serve as an opportunity for the country to showcase its closer alignment with China and Russia.

State media on Tuesday confirmed that a Russian military delegation led by Defense Minister Sergei Shoigu will also travel to Pyongyang to participate in celebration events.

A high-level Chinese delegation led by Politburo member Li Hongzhong will visit Pyongyang for the same reason, state media reported Monday. The last time a Chinese delegation was sent to Pyongyang for a similar purpose was to celebrate the country's founding on September 9, 2018, before the COVID-19 pandemic.

The top nuclear envoys from South Korea, the US and Japan on Tuesday notably held discussions on these developments related to North Korea's July 27 celebration events, including the visit by the Chinese delegation, according to South Korea's Ministry of Foreign Affairs.

"The three agreed to continue enhancing close communication and cooperation among South Korea, the United States and Japan to make North Korea realize that it will gain nothing from nuclear and missile development and provocations," said a ministry statement released Tuesday.

During the phone call, the three envoys discussed countermeasures in response to North Korea's ballistic missile launches, and they committed to "respond firmly to any provocations from North Korea."