SEOUL, South Korea >> North Korea fired its first intercontinental ballistic missile in three months on Wednesday, two days after it threatened “shocking” consequences to protest what it called provocative U.S. reconnaissance activity near its territory.

Some experts say North Korea likely launched its developmental, road-mobile Hwasong-18 ICBM, a type of solid-fuel weapon that is harder to detect and intercept than its liquid-fuel ICBMs. North Korean leader Kim Jong Un previously called the Hwasong-18 his most powerful nuclear weapon.

The missile fired from North Korea’s capital region around 10 a.m. flew about 1,000 kilometers (620 miles) at a maximum altitude of 6,000 kilometers (3,730 miles) before landing in waters between the Korean Peninsula and Japan, according to South Korean and Japanese assessments. They said the missile was launched on a high angle, in an apparent attempt to avoid neighboring countries.

South Korea’s military called the launch “a grave provocation” and urged North Korea to refrain from additional launches. Chief Japanese Cabinet Secretary Hirokazu Matsuno denounced North Korea’s repeated missile launches as “threats to the peace and safety of Japan, the region and international society.”

In a trilateral phone call, the chief nuclear envoys of South Korea, Japan and the U.S. agreed to sternly deal with North Korean provocations and boost their coordination to promote a stronger international response to the North’s nuclear and missile programs, according to Seoul’s Foreign Ministry.

The launch came while South Korean President Yoon Suk Yeol and Japanese Prime Minister Fumio Kishida are attending the NATO summit in Vilnius, Lithuania. In an emergency meeting of South Korea’s security council convened by video in Lithuania, Yoon warned North Korea would face more powerful international sanctions due to its illicit weapons programs.

North Korea’s ICBM program targets the mainland U.S, while its shorter-range missiles are designed to hit South Korea and Japan, both key American allies in northeast Asia.

Since 2017, North Korea has performed a slew of ICBM tests, but some experts say the North still has some technologies to master to possess functioning nuclear-armed missiles capable of reaching major U.S. cities.

The North’s most recent previous ICBM test was the first launch of the Hwasong-18 in April. After that launch, Kim said the missile would enhance the North’s counterattack capabilities and ordered the expansion of his country’s nuclear arsenal to “constantly strike extreme uneasiness and horror” in its rivals.

Missiles with built-in solid propellants would be easier to move and hide, making it difficult for opponents to detect their launches in advance. All of North Korea’s previous ICBM tests used liquid fuel.

Kim Dong-yub, a professor at the University of North Korean Studies in Seoul, said Wednesday’s launch appeared to be the North’s second flight-test of the Hwasong-18.

The launch, the North’s first weapons firing in about a month, came after North Korea earlier this week released a series of statements accusing the United States of flying a military spy plane close to its soil.

In a statement Monday night, Kim’s sister and top adviser, Kim Yo Jong, warned the United States of “a shocking incident” as she claimed that the U.S. spy plane flew over the North’s eastern exclusive economic zone eight times earlier in the day. She claimed the North scrambled warplanes to chase away the U.S. plane.

The U.S. and South Korea dismissed the North’s accusations and urged it to refrain from any acts or rhetoric that raised animosities.

“I would just say that we continue to urge (North Korea) to refrain from escalatory actions,” Matthew Miller, a spokesperson for the U.S. State Department, said Tuesday. “As a matter of international law, the (North Korea’s) recent statements that U.S. flights above its claimed exclusive economic zone are unlawful are unfounded, as high seas freedoms of navigation and overflight apply in such areas.”

North Korea has made numerous similar accusations over U.S. reconnaissance activities, but its latest statements came amid heightened animosities over North Korea’s torrid run of weapons tests since the start of last year. Some observers say the North wants to use an expanded weapons arsenal to wrest greater concessions in eventual diplomacy with its rivals.

“Kim Yo Jong’s bellicose statement against U.S. surveillance aircraft is part of a North Korean pattern of inflating external threats to rally domestic support and justify weapons tests,” said Leif-Eric Easley, a professor at Ewha University in Seoul. “Pyongyang also times its shows of force to disrupt what it perceives as diplomatic coordination against it, in this case, South Korea and Japan’s leaders meeting during the NATO summit.”

Kim Dong-yub, the professor, said Wednesday’s launch was likely made under the North’s previously scheduled weapons build-up programs to hone Hwasong-18 technologies, rather than a direct response to the NATO gathering or the alleged U.S. spy plane flight.

The Hwasong-18 is among an array of high-tech weapons that Kim Jong Un has vowed to introduce to deal with what he called escalating U.S. military threats. Other weapons on his wish-list are an ICBM with multi-warheads, a spy satellite and a nuclear-powered submarine. In late May, North Korea’s launch of its first spy satellite ended in failure, with a rocket carrying it plunging to the ocean soon after liftoff.

Some experts say North Korea could ramp up weapons tests around July 27, the date for the 70th anniversary of the signing of an armistice that ended the 1950-53 Korean War. North Kore calls the date “the V-Day” or “the War Victory Day.”

“Pyongyang might be manufacturing tensions ahead of its Victory Day to further strengthen solidarity domestically after having failed its first spy satellite launch in May and then justifying future provocations by first unleashing a stream of threats and harsh rhetoric about U.S. spy planes,” said Duyeon Kim, an adjunct Senior Fellow with the Center for a New American Security.

U.N. Security Council resolutions ban North Korea from engaging in any launches using ballistic technologies. But China and Russia, both permanent members of the council, blocked the U.S. and others’ attempts to toughen U.N. sanctions on North Korea over its recent ballistic missile tests.