North Koreaâs official news agency said Saturday that Kim Jong-un had called the test a âstern warningâ to the United States. He also boasted that the North was âcapable of the surprise launching of an intercontinental ballistic missile at any time and from anywhere and that all of the mainland United States is within the range of our missiles.â
The United States has gone to extraordinary lengths â feeding flawed parts into the North Korean production system and mounting internet attacks to cause test failures â to slow North Koreaâs missile program. A few hours before the test, Congress approved the latest round of sanctions to squeeze the North.
While there have been some tactical successes, they have not stopped the weapons program. And Mr. Kim, determined to show the United States that he would not waver from his goal, has stepped up the pace of testing. In his remarks on Saturday, Mr. Kim said that the threat of sanctions or military action against the North âonly strengthens our resolve and further justifies our possession of nuclear weapons.â
In a break with past practice, the White House turned out a statement in the name of President Trump, but it made no mention of the distance the missile flew or its implications. It read like many of President Barack Obamaâs and President George W. Bushâs statements at similar moments.
âBy threatening the world, these weapons and tests further isolate North Korea, weaken its economy, and deprive its people,â Mr. Trump said. âThe United States will take all necessary steps to ensure the security of the American homeland and protect our allies in the region.â
Mr. Trump hoped to end North Koreaâs provocations with the help of China, and he thought he had an agreement with President Xi Jinping to pressure Mr. Kim. But over the past two months, Mr. Trump discovered, as his predecessors did, that the Chinese are more concerned about preventing the collapse of North Koreaâs government, and the chaos that would ensue, than they are in trade and energy sanctions that might truly change its behavior.
On Saturday, the Chinese Ministry of Foreign Affairs condemned the North Korean missile test, but it also urged other countries to avoid responding in ways that could set off any tit-for-tat retaliation.
âChina opposes North Korea engaging launch activities that violate Security Council resolutions and the universal wishes of the international community,â a Chinese Foreign Ministry spokesman, Geng Shuang, said in comments issued on the ministryâs website.
Mr. Geng urged North Korea to abide by the United Nations Security Council resolutions banning its missile and nuclear tests, and said that North Korea should âhalt any actions that may lead to a further escalation of tensions on the peninsula.â But Mr. Geng added, âAt the same time, it is hoped that all parties act prudently, and prevent a spiraling escalation of tensions.â
Shi Yinhong, a professor of international relations at Renmin University in Beijing, said that the Chinese government would interpret the test as affirmation of its view that Mr. Trumpâs policies toward North Korea were failing.
But China has not been able to change Mr. Kimâs behavior either, Mr. Shi said. China has not demonstrated an ability âto persuade Kim Jong-un to abandon what he is determined to do,â he said.
For Mr. Trump, the launch poses one of the biggest challenges of his presidency. Like Bill Clinton, Mr. Bush and Mr. Obama before him, Mr. Trump declared that the North would not succeed in obtaining a missile that could put American cities at risk. âIt wonât happen,â he declared in a Jan. 2 tweet, not long after Mr. Obama warned him that the North would probably pose the most urgent national security threat he would face.
American officials, led by Defense Secretary Jim Mattis, have been careful not to threaten to carry out a pre-emptive strike on the Northâs nuclear and missile capabilities, which Mr. Mattis has warned could reignite the Korean War. Cyberattacks, while more politically palatable, are of uncertain effectiveness. And sanctions have done little.
Now, outside experts said, it has happened. David C. Wright, a senior scientist at the Union of Concerned Scientists, an anti-proliferation group in Cambridge, Mass., said in a blog post on Friday that the missile appeared to have an effective range of at least 6,500 miles â putting Los Angeles, Denver and Chicago well within range. He wrote that Boston and New York âmay be just within range, and Washington âmay be just out of range.â
But such estimates are always subject to uncertainty. North Koreaâs aim is famously poor and it is unclear how long it would take the country to build a workable nuclear warhead that can survive re-entry into the atmosphere.
And Dr. Wright cautioned that Western analysts have no idea how much the payload on the missile weighed. âIf it was lighter than the actual warhead the missile would carry,â he noted, the calculated ranges for a real warhead would be shorter.
The Pentagon confirmed only that the missile was an ICBM, which means that it was capable of traveling at least 5,500 kilometers, or about 3,400 miles. Pentagon officials said that it was airborne for more than 40 minutes.
Hours after the test, the United States and South Korea launched ballistic missiles off the east coast of the South on Saturday to test their abilities to counter the North. The drill involved the United States Army Tactical Missile System and the Southâs Hyunmoo-2 missile.
It was not disclosed how many missiles were launched, but a video released by the United Statesâ Eighth Army showed three fired from missile-launch vehicles.
The exercise was in direct response to the North Korean missile test, Pentagon officials said.
North Korea conducted its first test of an intercontinental ballistic missile, the Hwasong-14, on July 4, calling it a âgift package for the Yankees.â South Korean officials said that the July 4 test demonstrated that the missile was capable of reaching Alaska, but that it remained unclear whether the North had the capability of launching a nuclear strike against the contiguous United States.
On Saturday in Seoul, the South Korean military said in a statement the latest test involved âa more advanced ICBM-class missileâ than the July 4 launch.
The South Korean military said that Fridayâs missile was launched from Jagang Province, a mountainous north-central area of North Korea bordering China, at 11:41 p.m. local time.
South Koreaâs new president, Moon Jae-in, called an emergency meeting of his National Security Council and ordered his military to conduct joint ballistic missile tests with the United States military in a âstrong show of power,â his office said. Similar missile exercises were held after the Northâs July 4 launch.
The growing North Korean threat also prompted Mr. Moon to reverse his decision to halt deployment of an advanced United States missile defense system known as Thaad. In a statement issued early Saturday, he told his military to push ahead with it.
North Korea is a closed society, and the secrecy of its government makes it difficult to tell exactly how far its weapons programs have advanced. But experts believe it is not yet capable of making nuclear warheads suitable for mounting on ICBMs.
South Korean defense officials have said since the July 4 test that it was too early to determine whether North Korea had mastered long-range missile technology, especially re-entry, when a warhead must survive intense heat and the destruction of its outer shell as it plunges through the atmosphere from space.
An earlier version of this article misspelled the given name of North Korea’s leader. He is Kim Jong-un, not Kim Jung-un.