U.S. Is Watching North Korea for Signs of Lethal Military Action

North Korea’s leader, Kim Jong-un, could take some form of lethal military action against South Korea in the coming months after having shifted to a policy of open hostility, U.S. officials say.

The officials have assessed that Mr. Kim’s recent harder line is part of a pattern of provocations, but that his declarations have been more aggressive than previous statements and should be taken seriously.

While the officials added that they did not see an imminent risk of a full-scale war on the Korean Peninsula, Mr. Kim could carry out strikes in a way that he thinks would avoid rapid escalation.

They pointed to North Korea’s shelling of a South Korean island in 2010 as an example. The two sides exchanged artillery fire, resulting in the reported deaths of troops on both sides as well as civilians in the South, but both militaries soon stopped.

Jonathan Finer, the White House deputy national security adviser, said at an Asia Society forum in Washington on Thursday that North Korea had “chosen to continue going down a very negative path.”

Mr. Kim’s more aggressive posture has been evident through a series of actions this month. On Wednesday, the North fired several cruise missiles from its west coast into the sea, the South Korean military said. Mr. Kim’s government announced on Jan. 14 that it had tested a new solid-fuel intermediate-range missile tipped with a hypersonic warhead. And on Jan. 5, his military fired hundreds of artillery shells into waters near South Korean islands, forcing some residents to seek shelter.

At the same time, Mr. Kim has decided to formally abandon a longtime official goal of peaceful reunification with South Korea, the North Korean state news media announced on Jan. 16. Mr. Kim had signaled the move for months and said in a speech the day before that conciliatory references to unity with the Republic of Korea, as the South is officially known, must be removed from the Constitution.

“We can specify in our Constitution the issue of completely occupying, subjugating and reclaiming the R.O.K. and annexing it as a part of the territory of our ​republic in case a war breaks out on the Korean Peninsula,” Mr. Kim said.

He has repeatedly denounced the three-way security pact announced in August by President Biden, President Yoon Suk Yeol of South Korea and Prime Minister Fumio Kishida of Japan.

The confluence of Mr. Kim’s policy shift and the projectile firings has caught the attention of U.S. officials who monitor North Korea, which has a nuclear weapons program and is under harsh United Nations sanctions. Mr. Kim’s moves also appear to be shutting the door, for now, on any chance of diplomacy with the United States, which he has shunned since his face-to-face talks with President Donald J. Trump failed in 2019.

And U.S. officials say the North Korean leader is likely feeling emboldened because of his growing partnership with Russia.

“The statements and policy changes are part of a broader strategy to destabilize and create anxiety,” said Jean H. Lee, a fellow at the East-West Center in Honolulu. She added that she thought Mr. Kim could take military action in an area like the West Sea, or Yellow Sea, where there are South Korean islands — including the one that Mr. Kim’s father shelled in 2010 — and where the North disputes a maritime border.

Two North Korea experts argued in an article this month that the situation on the Korean Peninsula “is more dangerous than it has been at any time since early June 1950,” when Mr. Kim’s grandfather decided to invade the South.

In the article, which U.S. government analysts and policymakers have read, the authors wrote that based on their interpretation of recent statements, Mr. Kim had “made a strategic decision to go to war.”

But so far, U.S. agencies have not detected concrete signs that North Korea is gearing up for combat or a major war, according to American officials interviewed for this article, who spoke on the condition of anonymity to discuss intelligence and diplomatic matters.

One official said North Korea’s decision to send large numbers of older artillery shells and smaller numbers of more modern ballistic missiles to Russia for its war in Ukraine showed that Mr. Kim was not preparing for a prolonged conflict with the South. A leader planning for a major military operation would hoard his stocks of missiles and artillery shells, the official said.

A missile and artillery barrage of South Korea or a land invasion would almost certainly mean war with the United States. The American military defended South Korea during the Korean War, which never officially ended but halted when an armistice was signed in 1953. Nearly 30,000 U.S. troops are based in South Korea.

Mr. Kim probably believes he can control any escalation, U.S. officials said. When North Korea shelled Yeonpyeong Island in 2010, the South Korean military retaliated, but the two sides quickly ended their artillery exchange.

Earlier that year, 46 sailors died when a South Korean warship sank off the country’s west coast; an investigation by international experts concluded a few months after that the warship had been hit by a torpedo fired by a North Korean submarine. South Korea imposed sanctions on the North, which had denied any role in the episode, but did not carry out any military strikes. During naval skirmishes in 1999 and 2002, both Koreas were also careful not to escalate into a full-blown war by keeping their interactions proportional.

North Korea can decimate cities in South Korea and kill U.S. troops on the peninsula using conventional weapons. The South and the United States also have the means to quickly destroy Pyongyang, the North’s capital, and military sites across the country.

North Korea has enough fissile material, mostly highly enriched uranium, for about 50 to 60 nuclear warheads, said Siegfried S. Hecker, a scientist at Stanford University who co-wrote the recent article on Mr. Kim going to a war footing.

Robert Carlin, the other author and a former U.S. intelligence analyst on North Korea, said in an interview that they had concluded based on the North’s actions and official statements since 2021 that Mr. Kim had abandoned a decades-long policy of trying to normalize relations with the United States.

“We surprised ourselves by seeing how alarming this situation had turned,” Mr. Carlin said.

He said he believed North Korean military planners would favor a surprise attack, which commanders carried out when they invaded the South in 1950, to “knock the Americans mentally off-balance, knock everybody off-balance.”

The North Korean government seemed to be especially fixated on the U.S. military’s departure from Afghanistan in August 2021, which Mr. Trump had planned and Mr. Biden carried out. North Korean officials “portrayed it as American global retreat,” Mr. Carlin said.

Daniel Russel, a vice president at the Asia Society and a former top Asia official at the State Department, said Mr. Kim seemed intent on a strike that went well beyond the shelling in 2010. “We should be preparing for the prospect of Kim doing a shocking kinetic action,” he said.

Mr. Biden, Secretary of State Antony J. Blinken and other U.S. officials have spoken to their Chinese counterparts about trying to persuade North Korea to end its missile tests, which have increased in recent years. Although China helped North Korea evade sanctions, it did not want armed conflict in the region, U.S. officials said.

However, there are limits to China’s influence with North Korea — and it could be waning because of Mr. Kim’s moves to establish closer ties to President Vladimir V. Putin of Russia.

Wang Huiyao, the president of the Center for China and Globalization, a research group in Beijing, described the general situation as “very dangerous” and said that “all the parties involved should talk together.”

Two U.S. officials said Mr. Kim appeared to have strengthened his military and diplomatic position, and it would be surprising if he risked that — and his regime — in a war.

His military has improved its ballistic missile program with the frequent tests, they said, while Mr. Kim and Mr. Putin appeared to be forging a personal bond, starting with their meeting in the Russian Far East in September. North Korean state media has reported that Mr. Putin said he planned to visit the country soon.

The Biden administration has been trying since 2021 to persuade North Korea to engage in diplomacy. On Jan. 19, the State Department said in a statement that the United States still “seeks dialogue” with the North “without preconditions and harbors no hostile intent.”

But Mr. Carlin said Mr. Kim felt betrayed and humiliated by Mr. Trump during the failed diplomacy of 2019. And he said the North Koreans knew the American line about dialogue without preconditions was “an old talking point” that did not signal any potential change in U.S. policy, which is based on sanctions aimed at getting Pyongyang to abandon its nuclear weapons program.

“If they’ve decided they don’t trust the Americans to do anything useful at any time,” Mr. Carlin said, “why would they respond positively?”

Keith Bradsher contributed reporting from Beijing, and Choe Sang-Hun from Seoul.