Passersby watch a news report on North Korean missile launches at Yongsan Station in Seoul in March. (File Photo - Im Se-jun/The Korea Herald).

North Korea fired a long-range ballistic missile off its eastern coast toward Japan on Wednesday morning, when the leaders of South Korea and Japan were set to hold a separate summit later in the day on the sidelines of a NATO summit.

The intercontinental ballistic missile, or ICBM, was fired from the area of the capital city of Pyongyang toward the East Sea at around 10 a.m., South Korea’s Joint Chiefs of Staff said.

The missile was fired at a lofted angle and traveled around 1,000 kilometers before splashing down in waters of the East Sea, the JCS said in a statement without further details, adding that South Korean and US intelligence authorities have been analyzing the missile’s specifications.

Japan’s Chief Cabinet Secretary Hirokazu Matsuno said the missile landed around 250 km west of Okushiri island in Japan’s northernmost Hokkaido prefecture, reaching an altitude of over 6,000 km. The ICBM flew for 74 minutes, marking the longest-ever flight for a North Korean missile.

The missile launch occurred at a delicate moment, coinciding with the ongoing two-day NATO summit in Vilnius, Lithuania, attended by South Korean President Yoon Suk Yeol and leaders of other Asia-Pacific partners comprising Australia, Japan and New Zealand.

Yoon convened an emergency meeting of the standing committee of the National Security Council in Lithuania at 5:45 a.m. Eastern European Time on Wednesday following the ICBM launch, according to the South Korean presidential office.

"Given that North Korea conducted a provocation during the NATO summit, where global security cooperation is being discussed, I will call for the international community's strong solidarity on upcoming occasions, including the NATO summit today," Yoon was quoted by Kim Eun-hye, senior presidential secretary for public affairs, as saying.

Yoon was set to hold a summit with Japanese Prime Minister Fumio Kishida on the sidelines of the summit of the US-led security alliance.

Yoon additionally urged attendees to "take military and diplomatic measures, both between South Korea and the United States and independently, without a hitch," Kim added in the written statement.

Kim said Yoon told attendees to utilize the upcoming inaugural meeting of the new Nuclear Consultative Group -- which is set for next Tuesday in Seoul -- as the venue to strengthen extended deterrence.

The NCG was launched to enhance the viability of extended deterrence, which is the US’ commitment to deter or respond to coercion and external attacks on US allies and partners with the full range of its military capabilities, including nuclear weaponry.

The ICBM launch overlapped with the long-planned Trilateral Chief of Defense, or Tri-CHOD, meeting on Tuesday (Hawaii Standard Time) in Hawaii, where General Kim Seung-kyum, the chairman of South Korea's Joint Chiefs of Staff, was in attendance along with his counterparts from the United States and Japan. The meeting was held from 8 a.m. to 11 a.m. Wednesday, Korea Standard Time.

Experts also took note that the missile launch also followed North Korea's repeated warnings of possible military action in response to what they consider routine reconnaissance activities conducted by the United States on the Korean Peninsula.

The warnings were conveyed through three statements released on Monday and early Tuesday.

North Korea's Ministry of National Defense on Monday sent a "serious warning to all the US’ dangerous and provocative military actions," threatening that it cannot rule out the scenario of shooting down US spy aircraft flying over the East Sea.

Kim Yo-jong, the influential sister of North Korean leader Kim Jong-un on Tuesday warned in an English-language statement published by the state-run Korean Central News Agency that “US forces will experience a very critical flight” in case of a repeated illegal intrusion.

Kim claimed that the US Air Force's reconnaissance aircraft violated the airspace above the North Korean side's exclusive economic zone, or EEZ, in the East Sea of the Korean Peninsula. But the South Korean military explained that the EEZ permits freedom of navigation and overflight, and simply flying in such areas does not constitute intrusion.

Yang Uk, a research fellow at the Asan Institute for Policy Studies think tank in Seoul, assessed that the ICBM launch was intended to gain the upper hand over South Korea and the US.

North Korea sought to exploit the US' routine aerial reconnaissance activities as a justification to escalate tensions and conduct the missile launch, after the country's failed launch of what it claimed to be a military reconnaissance satellite stultified itself.

"As North Korea finds itself in a disadvantageous strategic situation, North Korea has consecutively released a series of statements and tough rhetoric," Yang said.

Yang noted that North Korea likely perceived a growing necessity to take military action given the upcoming first NCG meeting and the planned dispatch of the US Navy's nuclear-armed ballistic missile submarine to South Korea, as well as the 70th anniversary of signing the Korean Armistice Agreement on July 27. Pyongyang has traditionally celebrated July 27 as the "Day of Victory in the Great Fatherland Liberation War."

"North Korea launched the missile, using the intrusion of reconnaissance aircraft into the EEZ as a pretext since it can no longer afford to portray itself as being dragged along in the lead-up to the Day of Victory in the War," Yang added.

Wednesday's ballistic missile launch is the first since June 15, when North Korea launched two short-range ballistic missiles towards the East Sea. The recent ICBM launch marks the first such instance since April 13, when North Korea carried out the inaugural test-firing of its new solid-fuel Hwasong-18 ICBM.