SEOUL, South Korea (AP) – North Korea on Tuesday fired at least one ballistic missile, which South Korea’s military said was likely designed to be launched from a submarine, in what is possibly the most significant demonstration of the North’s military might since U.S. President Joe Biden took office.

The launch of the missile into the sea came hours after the U.S. reaffirmed an offer to resume talks on North Korea’s nuclear weapons program. It underscored how North Korea has continued to expand its military capabilities during the pause in diplomacy.

South Korea’s Joint Chiefs of Staff said in a statement it detected that North Korea fired one short-range missile it believed was a submarine-launched ballistic missile from waters near the eastern port of Sinpo, and that the South Korean and U.S. militaries were closely analyzing the launch.

Japan’s military said its initial analysis suggested that North Korea fired two ballistic missiles. Prime Minister Fumio Kishida said officials were examining whether they were submarine-launched.

Mr. Kishida interrupted a campaign trip ahead of Japanese legislative elections later this month and returned to Tokyo because of the launch. He ordered his government to start revising the country’s national security strategy to adapt to growing North Korean threats, including the possible development of the ability to pre-emptively strike North Korean military targets.

“We cannot overlook North Korea’s recent development in missile technology and its impact on the security of Japan and in the region,” he said.

Japanese Defense Minister Nobuo Kishi said one of the North Korean missiles reached a maximum altitude of 30 miles and flew on “an irregular trajectory” while traveling as far as 360 miles. He said the missile did not breach Japan’s exclusive economic zone set outside its territorial waters.

South Korean officials held a national security council meeting and expressed “deep regret” over the launch occurring despite efforts to revive diplomacy. A strong South Korean response could anger North Korea, which has accused Seoul of hypocrisy for criticizing the North’s weapons tests while expanding its own conventional military capabilities.

UN Secretary-General Antonio Guterres is concerned at the latest reported launches and again calls on North Korea’s leaders to comply with their obligations under UN Security Council resolutions and “swiftly resume diplomatic efforts towards sustainable peace and the complete and verifiable denuclearization of the Korean peninsula,” UN deputy spokesman Farhan Haq said.

The apparent site of the missile firing—a shipyard in Sinpo—is a major defense industry hub where North Korea focuses its submarine production. In recent years, North Korea has also used Sinpo to develop ballistic weapons systems designed to be fired from submarines.

Analysts had expected North Korea to resume tests of such weapons after it rolled out at least two new submarine-launched missiles during military parades in 2020 and 2021. There have also been signs that North Korea is trying to build a larger submarine that would be capable of carrying and firing multiple missiles.