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 offers the latest evidence of the United States’ declining presence in the region.
The South Korean decision on 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 Japan, America’s two closest Asian allies.
Those ties had reached their lowest point in years after Tokyo imposed a series of trade restrictions earlier this month targeting South Korea’s major exports. Japan took further action against Seoul by removing it from a list of trusted trade partners, and South Korea responded in kind.
But there had been signs in recent days that the two sides were seeking ways to ease the strains. In 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 had linked with Japan in urging Mr. Moon’s government not to pull out of the agreement. Stephen Biegun, an American envoy, met with South Korean officials earlier on Thursday and discussed the pact.
Seoul’s announcement, which came shortly after that meeting, took many observers by surprise.
Kim You-geun, first deputy chief of South Korea’s National Security Council, said Thursday that 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.”
There was no immediate response from the Japanese government.
A Pentagon spokesman, Lt. Col. Dave Eastburn, said the United States hoped that Japan and South Korea would work together to 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. Intel sharing is key to developing our common defense policy and strategy,” he said.
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 experts said 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.
Analysts in South Korea said they feared that Seoul’s decision to terminate the intelligence-sharing deal could hurt its alliance with Washington, which has long wanted both Seoul and Tokyo to work more closely to confront North Korea’s nuclear and missile threats and China’s growing influence in the region.
They noted that Seoul’s decision came despite Washington’s repeated appeals for South Korea and Japan to mend the growing rupture between its two allies.
“This is totally unwise. South Korea is turning itself into a black swan,” said Kim Sung-han, a former vice foreign minister of South Korea who teaches at Korea University in Seoul. “I fear a chill in the South Korea-U.S. relations because South Korea has itself severed a link in the security cooperation with the United States.”
Some analysts, though, said it was the Trump administration, which in pursuing an “America first” agenda has let alliances wane around the globe, that was to blame for the fracture in East Asia.
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 triliteralism in Northeast Asia,” said Ankit Panda, an adjunct senior fellow at the Federation of American Scientists.
“There was a complete lack of attention before this crisis hit,” Mr. Panda said.
In Japan, the South Korean decision was viewed as an unexpected turn by some, but others suggested that the administration of Prime Minister Shinzo Abe should have anticipated that Seoul would retaliate after Japan tightened restrictions on exports of certain chemicals and materials.
“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.”
He 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,” Mr. Watanabe said.
The collapse of the intelligence-sharing deal comes at a particularly sensitive time 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.
“We’re going to lose an important source of information-sharing between our two allies at a very dangerous time,” said Mr. Panda, the Federation of American Scientists fellow.
Mr. Panda said that South Korea was fundamentally re-evaluating its relationship with Japan. “I think the two countries can be fairly described as adversaries now,” said Mr. Panda. He added: “In Seoul, the idea is if we can do something that will hurt Japan more than it will hurt us, then it’s worth doing.”
Negotiating the intelligence-sharing agreement in the first place “was such a process to get in that it’s hard to imagine any South Korean government having an easy time getting back in, certainly not in the foreseeable future,” said Tobias Harris, an analyst of Japanese politics and economics at Teneo Intelligence, a political risk advisory firm.
The withdrawal, he said, will “foreclose the option of deepening political and security ties for a long time to come.”
Under the agreement, known as the General Security of Military Information Agreement, Japan and South Korea exchange sensitive military intelligence, such as tracking data about North Korea’s missile launches, rather than going through Washington, which has separate intelligence-sharing 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.
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 got worse 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, as 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.
Angry South Koreans responded with protests and widespread boycotts of Japanese goods, and Mr. Moon’s government downgraded Japan’s trade status. Lawmakers and protesters demanded that the intelligence-sharing agreement be scrapped.
The 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 by sharing information seamlessly.
The intelligence-sharing deal is automatically renewed annually unless one side informs the other of its intention of terminating it with a 90-day notice. This year, that deadline falls on Saturday.
South Korea’s decision came a day after its foreign minister, Kang Kyung-wha, and her Japanese counterpart, Taro Kono, met in Beijing but failed to narrow differences on how to mend the ties.
Any political gain Mr. Moon could win by seeking to punish Japan and catering to nationalistic sentiments could be short-lived if South Koreans grow tired of the prolonged strain with Tokyo and start questioning the wisdom of shaking the alliance with Washington, said Cheon Seong-whun, a former director of the Korea Institute for National Unification, a think tank 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.”