South Korea said on Thursday that it would abandon a military intelligence-sharing pact with Japan, a move that dramatically escalates tensions between the two countries and underscores the United States’ diminishing leadership in the region.
The South Korean decision on renewing the security agreement — a pact the United States had pushed in part to ensure tight monitoring of North Korea’s missile activity — had been awaited as a barometer of relations between Seoul and Tokyo, America’s two closest Asian allies.
Those ties had reached their lowest point in years after Tokyo imposed trade restrictions this month targeting exports to South Korea. Japan took further action against Seoul by removing it from a list of trusted trade partners, and South Korea responded in kind.
The flare-up punctuated decades of waxing and waning enmity between the two countries, rooted in Japan’s colonization of South Korea before World War II.
In recent days, there had been signs that the two sides were seeking ways to ease the strains, making the decision by Seoul a surprise to many.
During a major speech last week, President Moon Jae-in of South Korea sent conciliatory signals to Japanese leaders, saying that “we will gladly join hands” if Tokyo chooses dialogue.
The Trump administration urged Mr. Moon’s government not to abandon the agreement. Stephen E. Biegun, an American envoy, met with South Korean officials earlier on Thursday.
Kim You-geun, first deputy chief of South Korea’s National Security Council, said the South had chosen to terminate the intelligence-sharing deal because the trade restrictions had “caused an important change in security-related cooperation between the two countries.”
Mr. Kim added in a statement, “Our government has concluded that it does not conform with our national interest to maintain the agreement struck for the purpose of sharing sensitive military intelligence.”
Taro Kono, Japan’s foreign minister, called South Korea’s decision “extremely regrettable.”
“The relationship between Japan and South Korea is in a very severe situation with the series of extremely negative and irrational moves by South Korea, including the decision this time,” Mr. Kono said in a statement. “The Japanese government will continue to urge South Korea to respond sensibly, based on our consistent stand over various issues.”
A Pentagon spokesman, Lt. Col. Dave Eastburn, said the United States hoped that Japan and South Korea would resolve their differences.
“We are all stronger — and Northeast Asia is safer — when the United States, Japan and Korea work together in solidarity and friendship,” he said. “Intel sharing is key to developing our common defense policy and strategy.”
The collapse of the deal comes at a particularly sensitive moment in the region. North Korea has conducted six ballistic missile tests in about a month, and Japan and South Korea regularly share analysis about such tests with each other as well as with the United States.
“Our hope was that it would cut down the time that the United States had to play the middle man on intelligence sharing in a crisis,” said Kelly Magsamen, who helped work on the agreement when she was the principal deputy assistant secretary of defense for Asian and Pacific Security Affairs in the Obama administration. “It’s absolutely essential. In a military crisis, such as a potentially hostile ballistic missile launch, we aren’t going to have time to play referee between Tokyo and Seoul.”
Analysts said that in the immediate term, both Japan and South Korea would be able to obtain important intelligence information about North Korean missile launches through the United States. But they noted that the South Korean withdrawal effectively prevented closer cooperation in the future.
“My main worry is not necessarily the intelligence loss, but the symbolic difficulties of ever restarting serious security cooperation again,” said Jonathan B. Miller, senior fellow at the Japan Institute of International Affairs.
Washington has long wanted both Seoul and Tokyo to work more closely to confront North Korea’s nuclear and missile threats as well as China’s growing influence in the region. American officials have made repeated appeals for South Korea and Japan to mend the growing rupture between them.
Under the Trump administration, those relationships have gotten more complicated. As it pursues an “America first” agenda, the administration has let its alliances wane around the globe.
While President Trump and senior foreign policy officials have expressed concern about the growing split between Tokyo and Seoul, they have also said they will not play the role of mediator.
The end of the intelligence-sharing agreement “is an indictment of the fact that this administration hasn’t invested the resources necessary to build any solid basis for trilateralism in Northeast Asia,” said Ankit Panda, an adjunct senior fellow at the Federation of American Scientists.
Mr. Trump’s aides have spoken to reporters in Washington about the importance of the intelligence-sharing agreement. In late July, John R. Bolton, the national security adviser, called officials in Tokyo and Seoul to ask them to freeze their hostilities. Mr. Pompeo made the same request of their foreign ministers at a summit in Bangkok.
Mr. Trump has said he is not worried about Pyongyang’s launches of short-range ballistic missiles, and intends to continue diplomacy with Kim Jong-un, the North Korea leader, over its nuclear weapons program. Negotiators from the two sides, though, have yet to meet this summer.
Mr. Biegun, the special representative on North Korea, traveled to Japan on Monday for meetings and is now in South Korea. The State Department said his aim was to discuss strengthening coordination on getting North Korea to end its nuclear weapons program. Morgan Ortagus, a State Department spokeswoman, said Wednesday that she had no details about the trip.
South Korea’s relations with Japan soured late last year when Mr. Moon’s government took steps to effectively nullify a 2015 agreement his conservative predecessor had reached with Tokyo over the so-called comfort women, Korean women and girls who were forced or lured into brothels for Japanese soldiers during World War II. The 2015 deal was meant to lay that painful issue to rest, and Japan accused Mr. Moon of tearing the wounds open again.
Matters worsened when South Korea’s highest court ruled that Korean victims of forced labor under colonial rule could seek compensation from Japanese companies. In recent weeks, the discord over historical issues began bleeding into the countries’ trade ties.
Japan removed South Korea from its “white list” of most-trusted trading partners and tightened controls on three chemicals needed to make semiconductors and flat-panel displays, which are major South Korean exports. The move was seen as an attack on South Korea’s major electronics firms, most notably Samsung and LG, which are pillars of the country’s economy.
Angry South Koreans responded with protests and widespread boycotts of Japanese goods, like the fashion retailer Uniqlo, while Mr. Moon’s government downgraded Japan’s trade status. Lawmakers and protesters demanded that the intelligence-sharing agreement be scrapped.
In Japan, some suggested that the administration of Prime Minister Shinzo Abe should have anticipated that Seoul would retaliate after Japan tightened restrictions on exports.
“That was clearly a very careless mistake,” said Tsuneo Watanabe, a senior research fellow at the Sasakawa Peace Foundation in Tokyo. “They didn’t consider the South Korean regime or the psyche of Moon Jae-in.”
Mr. Watanabe said he hoped that Japan would be restrained enough not to escalate tensions further. “Maybe their business and ordinary constituencies are realistic enough to demand that they not retaliate,” he said.
South Korea’s decision came a day after its foreign minister, Kang Kyung-wha, and her Japanese counterpart, Mr. Kono, met in Beijing but failed to narrow differences.
The intelligence-sharing deal between South Korea and Japan, signed in late 2016, was reached as part of a broader American effort to ensure that the three countries respond more quickly and efficiently to threats from North Korea, China and Russia.
Under the agreement, known as the General Security of Military Information Agreement, Japan and South Korea exchange sensitive military intelligence, rather than going through Washington, which has separate deals with both nations.
Japan monitors North Korea with satellites, radar and surveillance aircraft, while South Korea’s geographical proximity and its intelligence-gathering on North Korea through spies, defectors and other human sources make its information valuable.
The deal is automatically renewed annually unless one side gives the other a 90-day termination notice. This year, that deadline falls on Saturday.
In practical terms, South Korea’s decision could hurt it more than Japan. Japan currently has more satellites trained on North Korea and the ability to track submarine movements by the North.
“South Korea is essentially shooting itself in the foot on this,” said Jeffrey Hornung, an analyst with the RAND Corporation. “They are making a self-inflicted wound here.”
“It’s purely a political move,” he added.
Any political gain for Mr. Moon, in catering to nationalist sentiments, could be short-lived if South Koreans tire of the prolonged strain with Tokyo and worry about the effect on the alliance with Washington, said Cheon Seong-whun, a former director of the Korea Institute for National Unification, a research group in Seoul.
“This is not a positive signal for the United States because South Korea is seen as shaking one pillar in Washington’s efforts to ensure that South Korea, Japan and the United States work closely to check the rise of China,” Mr. Cheon said. “In the long term, some people in the United States may start questioning whether South Korea is on their side or on China’s.”