SEOUL, South Korea — North Korea said on Tuesday that it had successfully conducted its first test of an intercontinental ballistic missile, claiming a milestone in its efforts to build nuclear weapons capable of hitting the mainland United States.
The announcement came hours after a launch that the United States military said sent the missile aloft for 37 minutes. That duration, analysts said, suggested a significant improvement in the range of the North’s missiles, and it might allow one to travel as far as 4,000 miles and hit Alaska.
In an initial statement, the United States Pacific Command described the weapon as an intermediate-range missile rather than an intercontinental ballistic missile. But South Korean and Japanese officials said they were studying the data to determine if it was an ICBM.
The missile took off from the Banghyon airfield in the northwestern town of Kusong and flew 578 miles before landing in the sea between North Korea and Japan, the South Korean military said in a statement.
The Japanese government said the missile landed in its so-called exclusive economic zone off its western coast. Under a series of United Nations Security Council resolutions, North Korea is prohibited from developing or testing ballistic missiles.
While the North is believed to have made significant progress in its weapons programs, experts believe it still has a long way to go in miniaturizing nuclear warheads for intercontinental ballistic missiles.
The missile test adds a volatile new element to the Trump administration’s efforts to curb North Korea’s nuclear ambitions, which have included naval drills off the Korean Peninsula and pressure on China, Pyongyang’s longtime ally. In a blunt phone call Sunday, President Trump warned President Xi Jinping of China that the United States was prepared to act alone against North Korea.
If the missile took 37 minutes to fly 578 miles, that would mean that it had a highly lofted trajectory, probably reaching an altitude of more than 1,700 miles, said David Wright, co-director of the Global Security Program at the Union of Concerned Scientists.
Such a missile would have a maximum range of roughly 4,160 miles, or 6,700 kilometers, on a standard trajectory, he said. North Korea said the missile, which it identified as the Hwasong-14, flew for 39 minutes.
“That range would not be enough to reach the lower 48 states or the large islands of Hawaii, but would allow it to reach all of Alaska,” Mr. Wright wrote in a blog post.
The missile looked like the longest-range missile that North Korea had ever tested, and its long flight time was “more consistent with an ICBM that can target Alaska and perhaps Hawaii,” said Jeffrey Lewis, director of the East Asia Nonproliferation Program at the Middlebury Institute of International Studies.
“It’s a very big deal — it looks like North Korea tested an ICBM,” he said by email. “Even if this is a 7,000-km-range missile, a 10,000-km-range missile that can hit New York isn’t far off.”
But analysts also cautioned that although they have been impressed by the rapid and steady progress in the North’s missile programs, the long flight time itself did not suggest that North Korea had mastered the complex technologies needed to build a reliable nuclear-tipped ICBM, such as the know-how to separate the nuclear warhead and guide it to its target.
By lofting some of its recent missiles to higher altitudes and letting them crash down toward the Earth at greater speeds, North Korea has claimed that it tested its “re-entry” technology, which can protect a nuclear warhead from intense heat and vibrations as it crashes through the Earth’s atmosphere. But it is still unclear whether the North has successfully cleared that technological hurdle, missile experts said.
Kim Dong-yub, a defense analyst at the Institute for Far Eastern Studies at Kyungnam University in Seoul, said that the Hwasong-12, which the North tested in May, flew 489 miles in 30 minutes, soaring to an altitude of 1,312 miles. Such a missile could deliver a standard 1,430-pound nuclear warhead over a range of 2,800 miles, not enough to reach Hawaii and Alaska, as North Korea claimed at the time.
North Korea’s test on Tuesday may have been intended to prove that its missiles could reach Hawaii and Alaska, Mr. Kim said.
North Korea announced the missile launch in a broadcast on state television after a series of patriotic music videos. “As a proud nuclear power that possesses not only nuclear weapons but also the most powerful ICBM that can target any part of the world, North Korea will root out the United States’ threat and blackmail of nuclear war and solidly defend the peace and stability of the Korean Peninsula and the region,” the North Korean statement said.
North Korea called the test “a momentous event in the history of the country” and said it had brought “great joy” to North Koreans.
Before the announcement, President Trump had noted the missile launch on Twitter, suggesting that it was time for China to act decisively against the North and “end this nonsense once and for all.” On Tuesday, Chinese officials criticized the missile test, saying it violated United Nations rules.
But at the same time, the Chinese government offered no signs that it was preparing to take more drastic action against the North, urging a return to diplomatic talks instead.
“I have to reiterate that the current situation in the Korean Peninsula is complicated and sensitive,” Geng Shuang, a spokesman for the Chinese Ministry of Foreign Affairs, said at a regular news conference in Beijing. “We hope all sides concerned can remain calm and restrained so that tensions can be eased as soon as possible.”
Mr. Trump is to meet this week with Mr. Xi at the Group of 20 meeting in Germany, and Cheng Xiaohe, an associate professor of international relations at Renmin University in Beijing, said the missile test would force them to find some kind of common ground on North Korea. He did not specify what that might be, but he suggested that it would now be more difficult for Mr. Xi to stand by Pyongyang.
“Certainly the test will change the game,” Mr. Cheng said. “The business-as-usual situation is over.”
Other analysts said the launch would put Mr. Trump’s administration in a precarious position, given that it had indicated that such a missile, capable of reaching parts of the United States, was a critical threshold. In January, Mr. Trump declared on Twitter “it won’t happen!”; the message set off a cascade of speculation on what exactly he meant.
“The important thing is that Donald Trump doesn’t let himself be backed into a corner and that he understands that there are long-term options to contain, constrain and deter the regime,” said Adam Mount, a senior fellow at the Center for American Progress in Washington.
The United States had hoped North Korea would stop short of developing a long-range missile that could reach its shores, Mr. Mount said. Now, he said, the United States and its allies will have to compromise on any expectation that North Korea will ever give up its nuclear program, he added.
“Talks can’t proceed from the presumption of denuclearization,” he said. “And we can’t coerce North Korea back to the negotiating table to prevent them from crossing a threshold they have already crossed.”