SEOUL, South Korea — North Korea’s attempt to put its first spy satellite into space failed Wednesday, a setback to leader Kim Jong Un’s push to boost his military capabilities as tensions with the United States and South Korea rise.

After an unusually quick admission of failure, North Korea vowed to conduct a second launch after it learns what went wrong. It suggests Kim remains determined to expand his weapons arsenal and apply more pressure on Washington and Seoul while diplomacy is stalled.

South Korea and Japan briefly urged residents in some areas to take shelter after the launch.

The South Korean military said it was salvaging an object presumed to be part of the crashed North Korean rocket in waters 125 miles west of the southwestern island of Eocheongdo. Later, the Defense Ministry released photos of a white metal cylinder it described as a suspected rocket part.

A satellite launch by North Korea is a violation of U.N. Security Council resolutions that ban the country from conducting any launch based on ballistic technology. Observers say North Korea’s previous satellite launches helped improve its long-range missile technology. North Korean long-range missile tests in recent years demonstrated a potential to reach all of the continental U.S., but outside experts say the North still has some work to do to develop functioning nuclear missiles.

The newly developed Chollima-1 rocket was launched at 6:37 a.m. at the North’s Sohae Satellite Launching Ground in the northwest, carrying the Malligyong-1 satellite. The rocket crashed off the Korean Peninsula’s western coast after it lost thrust following the separation of its first and second stages, the North’s official Korean Central News Agency said.

South Korea’s military said the rocket had “an abnormal flight” before it fell in the water. Japanese Chief Cabinet Secretary Hirokazu Matsuno told reporters that no object was believed to have reached space.

North Korean media said the country’s space agency will investigate what it calls “the serious defects revealed” by the launch and conduct a second launch as soon as possible.

“It is impressive when the North Korean regime actually admits failure, but it would be difficult to hide the fact of a satellite launch failure internationally, and the regime will likely offer a different narrative domestically,” said Leif-Eric Easley, a professor at Ewha University in Seoul. “This outcome also suggests that Pyongyang may stage another provocation soon, in part to make up for today’s setback.”

Adam Hodge, a spokesperson at the U.S. National Security Council, said in a statement that Washington strongly condemns the North Korean launch because it used banned ballistic missile technology, raised tensions and risked destabilizing security in the region and beyond.

The U.N. imposed economic sanctions on North Korea over its previous satellite and ballistic missile launches but has not responded to recent tests because China and Russia, permanent Security Council members now locked in confrontations with the U.S., have blocked attempts to toughen the sanctions.

Seoul’s military said it boosted military readiness in coordination with the United States, and Japan said it was prepared to respond to any emergency. The U.S. said it will take all necessary measures to ensure the security of the American homeland and the defense of South Korea and Japan.

After the launch was detected, the South Korean government sent text messages urging residents of a front-line island off the west coast to move to safer places. Officials in Seoul issued similar phone messages to city residents, but the country’s Interior and Safety Ministry later said the Seoul alerts were sent in error. Seoul’s mayor apologized for causing public confusion.

Japan activated a missile warning system for Okinawa prefecture in southwestern Japan, in the rocket’s suspected path. “Please evacuate into buildings or underground,” the Japanese alert said.

Japanese Defense Minister Yasukazu Hamada said Japan plans to keep missile defense systems deployed in its southern islands and in southwestern waters until June 11, the end of North Korea’s announced launch window.

KCNA didn’t provide details of the rocket or the satellite beyond their names. Experts earlier said North Korea would likely use a liquid-fueled rocket as most of its previously tested long-range rockets and missiles have.

Though it plans a fuller investigation, the North’s National Aerospace Development Administration attributed the failure to “the low reliability and stability of the new-type engine system applied to (the) carrier rocket” and “the unstable character of the fuel,” according to KCNA.

Gallery • 4 Photos

AHN YOUNG-JOON / Associated Press

A TV screen shows a file image of North Korea's rocket launch during a news program at the Seoul Railway Station in Seoul, South Korea, May 31. North Korea launched a purported rocket Wednesday, a day after the country announced a plan to put its first military spy satellite into orbit, South Korea's military said.

However, the spy satellite shown earlier in the country’s state-run media didn’t appear to be sophisticated enough to produce high-resolution imagery. Some outside experts said it may be able to detect troop movements and large targets such as warships and warplanes.

Recent commercial satellite imagery of the North’s Sohae launch center showed active construction, indicating North Korea plans to launch more than one satellite. In his Tuesday statement, Ri also said North Korea would test “various reconnaissance means” to monitor moves by the United States and its allies in real time.

With three to five spy satellites, North Korea could build a space-based surveillance system that allows it to monitor the Korean Peninsula in near real-time, according to Lee Choon Geun, an honorary research fellow at South Korea’s Science and Technology Policy Institute.

The satellite is one of several high-tech weapons systems that Kim has publicly vowed to introduce. Other weapons on his wish list include a multi-warhead missile, a nuclear submarine, a solid-propellant intercontinental ballistic missile and a hypersonic missile. In his visit to the space agency in mid-May, Kim emphasized the strategic significance of a spy satellite in North Korea’s standoff with the United States and South Korea.

Easley said Kim likely increased pressure on his scientists and engineers to launch the spy satellite after rival South Korea successfully launched its first commercial-grade satellite aboard its domestically built Nuri rocket earlier this month.

South Korea is expected to launch its first spy satellite later this year, and analysts say Kim likely wants his country to launch its spy satellite before the South to reinforce his military credentials at home.

After repeated failures, North Korea successfully put its first satellite into orbit in 2012 and a second one in 2016. The government said both are Earth observation satellites launched under its peaceful space development program, but many foreign experts believe both were developed to spy on rivals.

Observers say there has been no evidence that the satellites have ever transmitted imagery back to North Korea.

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Associated Press writer Mari Yamaguchi in Tokyo contributed to this report.