SEOUL, South Korea — North Korea fired what appeared to be a submarine-launched ballistic missile off its east coast on Saturday, the U.S. and South Korea said, the latest in a string of tests that are part of efforts by the North to advance technology capable of delivering nuclear warheads.

The missile was fired from a location near the North Korean coastal town of Sinpo, where analysts have previously detected efforts by the North to develop submarine-launched ballistic missile systems, said an official from Seoul’s Defense Ministry. The official, who didn’t want to be named because of office rules, couldn’t immediately confirm how far the missile traveled or where it landed.

South Korea’s Joint Chiefs of Staff said in a statement that it presumed the missile successfully ejected from the submarine’s launch tube, but failed in its early stage of flight. South Korea’s Yonhap news agency said that the missile likely flew only a few kilometers (miles) before exploding in midair, but the Defense Ministry official couldn’t confirm the report.

The U.S. Strategic Command also said that the missile was tracked over the sea between the Korean Peninsula and Japan, where it apparently fell.

“We strongly condemn this and North Korea’s other recent missile tests, which violate U.N. Security Council resolutions explicitly prohibiting North Korea’s launches using ballistic missile technology,” said Cmdr. Gary Ross, a Pentagon spokesman.

North Korea acquiring the ability to launch missiles from submarines would be an alarming development for rivals and neighbors because missiles from submerged vessels are harder to detect in advance. While security experts say it’s unlikely that North Korea possesses an operational submarine capable of firing missiles, they acknowledge that the North is making progress on such technology.

North Korea already has a considerable arsenal of land-based ballistic missiles and is believed to be advancing its efforts to miniaturize nuclear warheads mounted on missiles through nuclear and rocket tests.

U.S. Army Gen. Curtis M. Scaparrotti, NATO’s top military commander, told reporters Saturday that North Korea’s latest missile test represents a serious threat, both to the region and the U.S.

“With every launch, they’re getting better and they’re working out their problems,” said Scaparrotti, who until recently commanded U.S. forces in South Korea.

North Korea last test-fired a submarine-launched ballistic missile in April, calling it as a success that strengthened its ability to attack enemies with “dagger of destruction.” South Korean defense officials said then that the missile flew about 30 kilometers (19 miles) before likely exploding in midair.

The North also test-fired a submarine-launched ballistic missile on Dec. 25, but that test was seen as a failure, the South’s Joint Chiefs of Staff said. The North first claimed a successful submarine-launched missile test in May last year.