North Korea fired four missiles into the East Sea late Sunday evening, a move that provoked swift condemnation from international leaders.

Three of the missiles fell in Japan’s exclusive economic zone, flying about 620 miles before falling into the sea off the North Korean coastline. South Korean military officials are still working to determine exactly what type of missiles the North launched. Initial reports said the projectiles were possibly intercontinental ballistic missiles (ICBMs), but the South Korean military later said that was unlikely.

North Korean leader Kim Jong Un personally supervised the missile tests and ordered the country’s strategic missile defense branch “to keep highly alert as required by the grim situation in which an actual war may break out any time, and get fully ready to promptly move, take positions and strike so that it can open fire to annihilate the enemies,” North Korean state news agency KCNA reported, according to Reuters.

“In the hearts of artillerymen ... there was burning desire to mercilessly retaliate against the warmongers going ahead with their joint war exercises,” KCNA said, referencing joint military drills conducted this month between South Korea and the U.S.

The launches drew fierce condemnation.

“The launches are clearly in violation of (UN) Security Council resolutions. It is an extremely dangerous action,” Japanese Prime Minister Shinzo Abe said in parliament, according to Reuters.

A spokesman for the State Department said the U.S. condemns the launches and is prepared to defend America and its allies from attack.

“We are prepared to use the full range of capabilities at our disposal against this growing threat,” Mark Toner said, according to The Associated Press.

U.S. National Security Adviser H.R. McMaster also spoke with his South Korean counterpart Kim Kwan-jin and both countries agreed to work together to impose pressure and sanctions on Pyongyang, per the AP.

Frederika Mogherini, the European Union’s foreign affairs chief, called the launches “illegal,” and urged North Korea’s leaders to re-engage in dialogue with the international community.

“The [Democratic People’s Republic of Korea] must halt all launches using ballistic missile technology and abandon its ballistic missile programmes in a complete, verifiable and irreversible manner, as required by the UN Security Council,” she said.

Chinese Foreign Ministry spokesman Geng Shuang said China had taken note of North Korea’s latest action. “All sides should exercise restraint and not do anything to irritate each other to worsen regional tensions,” Geng said, according to Reuters.

Korean Central News Agency/Reuters The North Korean military parades in this undated photo released by North Korea's Korean Central News Agency on Oct. 12, 2015.

North Korea threatened last week to unleash a “merciless” response to joint U.S.-South Korea military exercises known as Foal Eagle.

The Pentagon said on Friday that about 3,600 U.S. service members joined 28,000 U.S. troops already based in South Korea for the drills.

Pentagon spokesman Navy Capt. Jeff Davis also stressed that the ground, air, naval and special operations field exercises, which last two months, are an annual occurrence.

“These exercises are defensive in nature, and they have been carried out regularly, openly and transparently for nearly 40 years,” Davis said.

KCNA KCNA / Reuters North Korean leader Kim Jong Un visited Mangyongdae Revolutionary School.

North Korea’s missile program is a top priority for U.S. President Donald Trump’s new administration.

Pyongyang has intensified its testing since the ascension of Kim Jong Un as supreme leader in 2011. The country executed two nuclear tests in 2016. And earlier this year, Kim Jong Un told the country in his annual New Year’s Day address that Pyongyang was “actively progressing” on developing long-range weaponry, which could possibly reach the United States. Kim declared North Korea to be a “military power of the East that cannot be touched by even the strongest enemy.”

“It won’t happen!” Trump tweeted in response to Kim’s pledge to test an ICBM.

The United Nations has subjected North Korea to harsh sanctions in an effort to stifle the country’s nuclear program, but the penalties have done little to deter development.

This article has been updated throughout.