North Korea on Thursday fired a ballistic missile off its east coast, after the country warned it would take “fierce” military action against US efforts to strengthen its extended deterrence posture against Pyongyang.

A short-range ballistic missile was fired from an area around the coastal city of Wonsan in Kangwon Province toward the East Sea at around 10:48 a.m. local time, South Korea’s Joint Chiefs of Staff said in a statement.

The short-range ballistic missile traveled about 240 kilometers at a speed of Mach 4 and an altitude of around 47 km, the JCS said in a statement, adding that South Korean and US intelligence authorities were still analyzing the missile's specifications.

“Our military is maintaining a full readiness posture in close coordination with the US in preparation for additional provocation by North Korea while tracking and monitoring related moves,” the JCS added.

The missile -- which the military sees as a solid-propellant short-range ballistic missile -- fired toward a target on an small uninhabited island in the waters off Kilju County, North Hamgyong Province, a military source, who wished to remain anonymous due to the sensitive nature of the issue, said.

North Korea’s ballistic missile launch came after South Korea and the US conducted “combined missile defense drills” on Thursday, according to the unnamed source.

Aegis destroyers belonging to the South Korean and US navies and other military assets participated in the drills which were previously scheduled, the source said declining to share further details including the scale, location and period of the drills.

The source underscored that South Korea and the US have continued to stage missile defense drills to enhance their readiness and defense posture against escalating North Korean missile threats.

But The Korea Herald learned that the South Korean military thought that North Korea was not likely to be aware of the missile defense drills staged Thursday, mainly due to the lack of surveillance and reconnaissance assets.

South Korea and the US also held a senior-level dialogue to discuss how to reinforce US extended deterrence and committed to coming up with effective measures to prepare for North Korea nuclear and missile threats on Thursday afternoon in Seoul.

The meeting was held after Richard Johnson, US deputy assistant secretary of defense for nuclear and countering weapons of mass destruction policy, briefed South Korean senior defense officials on the recently released US Missile Defense Review and Nuclear Posture Review.

'Serious warning'
The ballistic missile launch conspicuously came hours after North Korea’s foreign minister Choe Son-hui sent a “serious warning” against the outcomes of the trilateral summit among South Korea, the US and Japan held on Sunday on the sidelines of the East Asia Summit in Phnom Penh, Cambodia.

“The recent tripartite talks will finally result in bringing the situation on the Korean peninsula to an unpredictable phase,” Choe said in an English-language statement.

Choe denounced the three countries for discussing ways to strengthen US extended deterrence to South Korea and Japan and warning of a “strong and resolute response” in the event of North Korea’s seventh nuclear test. Choe claimed that the three countries labeled North Korea’s “legitimate and just military counteractions, incited by their war drills for aggression, as ‘provocation.’”

The leaders of South Korea, the US and Japan strongly condemned North Korea’s unprecedented number of ballistic missile launches, including multiple intercontinental ballistic missile launches, as well as artillery fire and other military action, saying they “pose a grave threat to the peace and security on the Korean Peninsula and beyond” in the joint statement issued after the summit.

In the statement, US President Joe Biden reaffirmed that the US commitment to reinforce extended deterrence to South Korea and Japan will only strengthen as the “regional security environment grows more challenging.”

Extended deterrence is the US commitment to deter or respond to coercion and attacks on US allies and partners. The US nuclear umbrella is one means the US offers to achieve extended deterrence.

North Korea’s foreign minister said strengthening US extended deterrence and combined military exercises increasingly frequently staged on and around the Korean Peninsula are “foolish acts that will bring more serious instability to the US and its allies.”

Choe warned that North Korea will take tit-for-tat military actions corresponding to the moves by the US and allies to reinforce their deterrence and readiness posture against North Korea.

“The keener the US is on the ‘bolstered offer of extended deterrence’ to its allies and the more they intensify provocative and bluffing military activities on the Korean peninsula and in the region, the fiercer the DPRK’s military counteraction will be, in direct proportion to it,” Choe said in the statement, referring to North Korea as its official name. “And it will pose a more serious, realistic and inevitable threat to the US and its vassal forces”

North Korea’s foreign minister warned that the “US will be well aware that it is gambling for which it will certainly regret.”

What does it mean, what is next?
Seoul-based North Korea experts said North Korea’s press statement reaffirmed the country’s “principle of strength-for-strength and head-on confrontation.”

Jung Dae-jin, a professor at Halla University in Gangwon Province, said the statement aimed to “explicitly express its dissatisfaction over the absence of the strategy to tip the balance” and get out of the current escalatory cycle at the trilateral summit.

Pyongyang also sought to “continuously reinforce the legitimacy of its principle of strength-for-strength and make a stepping stone to move into the next phase of confrontation.”

Echoing the view, Lim Eul-chul, a professor of North Korean studies at Kyungnam University in Seoul, said Choe’s statement showed North Korea’s intent to “take tit-for-tat actions against trilateral moves to step up military cooperation and reinforce US extended deterrence while standing by its gun.”

“North Korea’s ballistic missile launch right after Choe Son-hui’s statement is assessed as showing its intent to continuously put pressure on South Korea, US and Japan by creating a security crisis constantly and to gain the upper hand in taking military actions,” Lim said. “Against that backdrop, North Korea will ratchet up tensions recurrently by continuing to make military provocations including ballistic missile launches.”

Lim said the foreign minister’s statement is “North Korea’s official warning against the recent South Korea-US-Japan trilateral agreement on stepping up military cooperation and strengthening US extended deterrence.”

Cheong Seong-chang, director of the Center for North Korean Studies at the Sejong Institute, also took note that the press statement was issued under the name of Choe, who “has actively represented Kim Jong-un's intentions and has been in charge of North Korea’s diplomacy toward the US and western countries.”

Cheong forecasted that the security situation on the Korean Peninsula will be further aggravated in light of Choe’s reaffirmation of the “principle of strength-for-strength.”

“North Korea is expected to further escalate tensions by launching mid to long-range missiles or intercontinental ballistic missiles at a normal angle toward the Pacific Ocean or launching reconnaissance satellites in order to incapacitate US extended deterrence.”