North Korean leader Kim Jong Un visited Mangyongdae Revolutionary School and planted trees with its students last week. (KCNA/Reuters)

North Korea launched four missiles Monday morning, a provocative barrage that coincided both with joint U.S.-South Korean military exercises on the southern half of the peninsula and with the opening of the annual National People’s Congress in China.

The launches follow a remarkable month in which Kim Jong Un’s regime tested a solid-fuel rocket that it says is part of an intercontinental ballistic missile capable of hitting the United States and in which the regime is accused of assassinating the leader’s half brother.

Both actions have angered allies and adversaries in the region, and Monday’s launches will only exacerbate that.

“Every year this time, they try to do something to defy the exercises,” said Bruce Bennett, a North Korea expert at the Rand Corp. in California. “This time, I think they’re also interested in making a statement to the Chinese and to let Beijing know this coal ban is going to hurt,” he said, referring to Beijing’s decision last month to stop importing coal from North Korea, cutting off a major economic lifeline.

The four missiles were fired from a known launch site on North Korea’s west coast, not far from the border with China, at 7:36 a.m. local time. They flew more than 600 miles across the country before splashing into the sea between Japan and the Korean Peninsula, the South’s Joint Chiefs of Staff said in a text message to local reporters.

The joint chiefs initially suspected that at least one of the projectiles might have been an intercontinental ballistic missile capable of hitting the United States’ West Coast, but later backed away from that analysis. A U.S. defense official said the Pentagon does not think the missile was an ICBM.

The U.S. Strategic Command said its systems detected and tracked the projectile but “determined the missile launch from North Korea did not pose a threat to North America.”

Regardless, the launches have ratcheted up the tensions in the region.

“South Korea strongly condemns North Korea’s missile launch today as a direct challenge and grave provocation despite warnings by the international community,” Hwang Kyo-ahn, the prime minister who is acting president, said during an emergency meeting of the national security council. “North Korea’s nuclear missile provocation is a real and imminent threat against the lives and safety of South Koreans.”

In Japan, the government said three of the missiles had landed perilously close, splashing down within its exclusive economic zone and within about 200 miles of its coastline in Akita prefecture.

“These missile launches clearly show that North Korea has developed a new threat,” a visibly worried Prime Minister Shinzo Abe told reporters in Tokyo. “We will collect information and strongly protest to North Korea.”

Bennett of Rand said the range of the missiles could have served as a warning to China. The missiles had 12 of China’s 20 largest cities within reach, he said.

China expressed its dismay over the launch, with a Foreign Ministry spokeswoman saying it “opposes” launches that undermine U.N. resolutions. Russia, meanwhile, was more blunt, describing itself as “seriously worried” about the launches which raise tensions in the region.

North Korea has repeatedly claimed to be working on an ICBM capable of reaching the west coast of the United States and has been making observable progress toward this goal. In his New Year’s address, Kim said North Korea had “entered the final stage of preparation for a test-launch of an intercontinental ballistic missile.”

Regardless of whether Monday’s launch was an ICBM, it is just a matter of time until North Korea succeeds in its goal of making one, said Jeffrey Lewis, director of the East Asia Non-Proliferation Program at the Middlebury Institute of International Studies at Monterey in California.

“It doesn’t matter if it’s today or tomorrow or next week or next year — that’s where this is heading,” Lewis said. “But we have no plan other than saying this is unacceptable or that it won’t happen,” he added, referring to a tweet from President Trump earlier this year.

After Kim’s statement in a Jan. 1 address that North Korea was working on its ICBM program, Trump tweeted: “It won’t happen!”

His administration is reviewing its policy toward North Korea, which was characterized as “strategic patience” during the Obama administration — waiting for sanctions to hurt and a humbled Kim to come to the negotiating table.

The latest provocation came as large-scale military exercises, involving more than 320,000 South Korean and U.S. troops and high-tech U.S. firepower, continue in South Korea. They began last week and will continue through the end of April.

In the past year or two, the exercises have become more overtly offensive, with the two militaries practicing “decapitation strikes” on the North Korean leadership.

North Korea denounced the exercises and warned last week that it was ready to retaliate. North Korea “will never remain a passive onlooker to the new U.S. administration overtly revealing its intention to put military pressure on [North Korea] and invade it while crying out for ‘peace by dint of strength,’ ” the state-run Korean Central News Agency reported in a statement it attributed to the Foreign Ministry.

North Korea last month launched an intermediate-range missile, its first since Trump was elected president. The missile appeared to show significant technological advances, with upgraded power and range, and analysts said it could mark another step in the push toward the capacity to hit Alaska or Washington state.

After that, Kim’s regime is suspected of ordering the assassination on the leader’s half brother, Kim Jong Nam, who was attacked with a chemical weapon at the airport in Kuala Lumpur, Malaysia, and died within 20 minutes.

The assassination led the Trump administration to cancel visas for North Korean diplomats to go to New York for meetings with former U.S. officials involved in North Korea policy, which would have been the first time in more than five years that such a meeting had taken place on U.S. soil.

Yoonjung Seo in Seoul, Yuki Oda in Tokyo and Missy Ryan in Washington contributed to this report.