SEOUL, South Korea >> North Korea fired a ballistic missile from a submarine off its east coast into the sea, the South Korean military said, at a time of heightened tensions between the two Koreas.

North Korea launched the missile from a submarine off the eastern coastal town of Sinpo on Wednesday morning, South Korea’s Joint Chiefs of Staff said in a statement. The launch comes just two days after the U.S. and South Korea began their annual joint military exercises that the North considers a rehearsal for an invasion.

(The missile was tracked over and into the Sea of Japan, approximately 300 miles off the coast of North Korea, U.S. Pacific Command said in a release. The North American Aerospace Defense Command determined the missile launch did not pose a threat to North America.

“Our commitment to the defense of our allies, including the Republic of Korea and Japan, in the face of these threats, is ironclad,” Pacific Command said. “We remain prepared to defend ourselves and our allies from any attack or provocation. We call on North Korea to refrain from actions that further raise tensions in the region and focus instead on taking concrete steps toward fulfilling its commitments and international obligations.”)

North Korea has previously fired several submarine-launched ballistic missiles into the sea, but outside experts said the North has yet to acquire operational submarine-launched missiles capable of striking distant targets like the mainland U.S.

The North’s acquiring the ability to launch missiles from submarines would be an alarming development because missiles fired from submerged vessels are harder to detect in advance.

The North’s latest missile launch comes at a time of intensified animosities between the rival Koreas over the defection of a senior North Korean diplomat in London and a U.S. plan to install a sophisticated missile defense system in South Korea. On Monday, South Korea and the United States also kicked off the annual Ulchi Freedom Guardian exercises, prompting North Korean threats of retaliation.

About 28,500 U.S. troops are based in South Korea to help deter potential aggression from North Korea, a legacy of the 1950-53 Korean War that ended with an armistice, not a peace treaty.

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Star-Advertiser reporter William Cole contributed to this story.

North Korea usually responds to the regular South Korea-U.S. military drills with weapons tests and fiery warlike rhetoric.