North Korea conducts an "important final-stage test" at Sohae Satellite Launching Ground in Cholsan, North Pyongan Province, for the development of a reconnaissance satellite, in this Dec. 19, 2022, file photo carried by the North's official Korean Central News Agency. Yonhap

North Korea fired an intercontinental ballistic missile (ICBM) into the East Sea on Wednesday, the South Korean military said, after the recalcitrant regime warned of military action over U.S. spy aircraft operations earlier this week.

The Joint Chiefs of Staff (JCS) said it detected the launch from an area in or around Pyongyang at about 10 a.m., and the missile, fired at a lofted angle, flew around 1,000 kilometers before splashing into the water.

The North's first ICBM launch in about three months came amid tensions heightened by Pyongyang's tough rhetoric against the United States, a move seen as aimed at firming up internal unity and building a rationale for provocations.

"The intelligence authorities of South Korea and the U.S. are conducting a comprehensive assessment regarding (the missile's) specifics," the JCS said in a text message sent to reporters.

President Yoon Suk Yeol, who is in Lithuania to attend a North Atlantic Treaty Organization (NATO) summit, presided over an emergency meeting of the National Security Council and vowed to strengthen deterrence in cooperation with the U.S., according to his office.

Yoon is expected to use his attendance at the summit to elicit international support to counter evolving North Korean nuclear and missile threats.

The South Korean and U.S. militaries held a coordination meeting right after the launch, and affirmed they will further solidify their combined defense posture against "any North Korean threats and provocations," the JCS said.

The JCS strongly condemned the launch and urged the North to immediately stop such launches, calling the latest launch an "act of significant provocation" that not only harms peace and stability on the Korean Peninsula but also in the international community.

This photo shows a U.S. U-2S reconnaissance aircraft landing at Osan Air Base in Pyeongtaek, Monday. Yonhap

It said the military will maintain a "firm" readiness posture based on "overwhelming" capabilities to respond to any provocations by North Korea.

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The North's last long-range missile launch took place April 13, involving a Hwasong-18 solid-fuel ICBM. Just last month, the North fired two short-range ballistic missiles in an apparent protest over a series of massive South Korea-U.S. live-fire drills.

On Monday and Tuesday, Kim Yo-jong, the powerful sister of North Korean leader Kim Jong-un, issued sharp-tongued statements claiming that U.S. military spy aircraft "intruded" into the area over the North's exclusive economic zone (EEZ).

Kim warned that the North will take "clear and resolute" actions against U.S. surveillance flights within the North's "economic water zone," claiming a "shocking" incident could occur.

The South Korean military has dismissed Kim's remarks, saying freedom of navigation and overflight are ensured in the EEZ.

Kim's statements came after the North's defense ministry on Monday denounced a U.S. plan to send a strategic nuclear submarine to the Korean Peninsula in the near future for the first time since 1981, warning the move could "incite the worst crisis of nuclear conflict in practice."

Washington had pledged to send a nuclear ballistic missile submarine to the peninsula in a joint declaration issued by Yoon and U.S. President Joe Biden during their summit in April as part of efforts to deter Pyongyang's military threats.

This week's ICBM launch is expected to add impetus to the efforts by Seoul and Washington to reinforce the credibility of America's extended deterrence commitment to using the full range of its military capabilities, including nuclear, to defend its ally.

As part of their deterrence efforts, the allies are set to hold the inaugural session of the Nuclear Consultative Group (NCG) in Seoul on Tuesday. The creation of the NCG was announced in the summit declaration in April.

The missile provocation may also help accelerate three-way cooperation efforts among the allies and Japan, including an ongoing push for the trilateral sharing of North Korean missile warning data in real time, according to observers.

The North's latest saber-rattling followed its failed launch of a space rocket carrying its first military reconnaissance satellite in late May. The rocket crashed into the Yellow Sea after an "abnormal starting" of the second-stage engine, according to the North's state media.

Observers said the latest launch could be intended to drum up internal unity after the failed launch and ahead of the 70th anniversary of the signing of the armistice that ended the 1950-53 Korean War on July 27, celebrated as Victory Day in North Korea.

"After the failed spy satellite launch, the North Korean regime appears to be trying to turn the situation around by firing an ICBM, a card to pressure the U.S.," said Shin Jong-woo, a senior analyst at the Korea Defense Security Forum. (Yonhap)