SEOUL — North Korea launched two ballistic missiles off its east coast on Wednesday, the country’s first ballistic missile test in six months and a violation of multiple United Nations Security Council resolutions that ban North Korea from conducting such tests.
Hours after the missiles were launched, South Korea announced that its president, Moon Jae-in, had just attended the test of the country’s first submarine-launched ballistic missile, making South Korea the seventh country in the world to operate S.L.B.M.s, after the United States, Russia, China, Britain, France and India.
The missile tests by both Koreas on the same day dramatically highlighted the intensifying arms race on the Korean Peninsula as nuclear disarmament talks with Washington remained stalled. They also underscored the growing concern over regional stability, with Prime Minister Yoshihide Suga of Japan calling the North Korean missile launch “outrageous” and a threat to peace.
In its announcement, South Korea also revealed that it had successfully developed a supersonic cruise missile and a long-range air-to-land missile to be mounted on the KF-21, a South Korean supersonic fighter jet, and that it had developed a ballistic missile powerful enough to penetrate North Korea’s underground bunkers.
The North’s missile launch occurred a day after the special envoy from the United States urged the country to resume nuclear disarmament talks, saying that the United States had no “hostile” intent toward Pyongyang. Neighboring countries have also stepped up efforts to get North Korea to return to the negotiating table.
North Korea conducted its previous ballistic missile test in March and test-fired what it called newly developed long-range cruise missiles over the weekend. The United States has not imposed fresh sanctions in response to the North’s short-range ballistic missiles in recent years. When North Korea resumed testing of short-range ballistic missiles in 2019, Donald J. Trump, then the president, dismissed them for being short range.
“Rather than strengthen sanctions and military exercises, the allies have emphasized a willingness for dialogue and humanitarian cooperation,” said Leif-Eric Easley, a professor of international studies at Ewha Womans University in Seoul. “The problem with less than robust responses to North Korea’s tests is that deterrence can be eroded while Pyongyang advances its capabilities and normalizes its provocations.”
The Biden administration has said it would explore “practical” and “calibrated” diplomacy to achieve the goal of the complete denuclearization of the Korean Peninsula. North Korea has yet to respond to the invitation to dialogue.
The North Korean missiles on Wednesday — launched from Yangdok, in the central part of the country — flew 497 miles and reached an altitude of 37 miles before landing in the sea between North Korea and Japan, the South Korean military said. South Korean and United States defense officials were analyzing the data collected from the test to determine exactly what type of ballistic missiles were used, it said.
Japan’s Ministry of Defense issued a statement saying that it “assumed” the missile did not reach the country’s territorial waters or its exclusive economic zone.
The news of the North Korean missile test broke shortly after Foreign Minister Wang Yi of China, North Korea’s biggest supporter and only remaining major trading partner, finished a meeting with his South Korean counterpart, Chung Eui-yong, in Seoul.
“It’s not just North Korea, but other countries as well that engage in military activities,” Mr. Wang said when asked by reporters to comment on the North’s weekend cruise-missile test. “We must all work together to resume dialogue. We all hope to contribute to peace and stability on the Korean Peninsula.”
Mr. Wang didn’t elaborate, but the United States and South Korea conducted joint military exercises last month. North Korea has accused Washington and Seoul of preparing to invade the North, and usually counters joint military drills between the two allies with its own military exercise or weapons tests.
“The United States has no hostile intent toward” North Korea, Sung Kim, the Biden administration’s special envoy, said on Tuesday in Tokyo, where he met with representatives from Japan and South Korea to discuss the North’s arsenal. He said Washington hoped that North Korea would “respond positively to our multiple offers to meet without preconditions.”
The latest tests showed that North Korea continued to improve its arsenal of missiles despite a series of resolutions from the United Nations Security Council that banned North Korea from developing or testing ballistic missiles and nuclear weapons.
Tensions on the Korean Peninsula rose sharply in 2017, when North Korea tested three intercontinental ballistic missiles and conducted its sixth underground nuclear test, leading to the sanctions from the United Nations. After the tests, the country claimed an ability to target the continental United States with a nuclear warhead.
Mr. Trump met with Kim Jong-un, the North Korean leader, three times between 2018 and 2019, but Mr. Trump and Mr. Kim failed to reach an agreement on lifting sanctions or rolling back the North’s nuclear and missile programs. Mr. Kim has since vowed to boost his country’s weapons capabilities.
With the recent tests, “North Korea is seeking to increase its leverage in coming talks” with Washington, said Lee Byong-chul, a North Korea expert at Kyungnam University’s Institute for Far Eastern Studies in Seoul.
By timing its latest test to Mr. Wang’s visit to Seoul, North Korea also appeared to “express discontent with Beijing” that it was not providing enough economic assistance during the coronavirus pandemic, Mr. Lee said. North Korea’s economy, already battered by years of devastating international sanctions, has suffered greatly as trade with has China plummeted in the pandemic.
Motoko Rich contributed reporting from Tokyo.