SEOUL, South Korea — Already-high tensions spiked on the Korean Peninsula as North Korea test-fired a missile from a submarine, a day after the U.S. announced plans to deploy an advanced missile defense system in the South.

The plan to have the Terminal High-Altitude Area Defense system, known as THAAD, operational by the end of next year also raised the stakes for regional security.

China reacted angrily. Analysts said the decision was likely to push Beijing and Washington farther apart at a time when cooperation is needed to face the growing threat from the North, and China is aggressively pursuing claims on disputed islands and reefs to the south and east.

Kim Joon Hyung of South Korea’s Handong Global University said the deployment of THAAD was creating a new Cold War-style scenario.

“The U.S. seems to be taking a hard-line policy toward China,” he said. “Relations between the U.S. and China are likely to get worse because of the deployment … while relations among China, Russia and North Korea are likely to be strengthened.”

South Korean military officials said a missile was apparently successfully launched Saturday from a submarine, the second such launch near the North Korean port town of Sinpo, but it failed in its early stage of flight.

The Yonhap news agency, citing South Korea’s Joint Chiefs of Staff, reported the missile was believed to have exploded at an altitude of about 6 miles. The U.S. Strategic Command said its systems tracked a presumed KN-11 submarine-launched ballistic missile Saturday over the Sea of Japan, where it apparently fell.

It was the latest in a string of missile tests that have seen limited success. But officials and analysts warn that the North learns lessons from failures.

“With every launch, they’re getting better and they’re working out their problems,” said Army Gen. Curtis M. Scaparrotti, NATO’s top military commander and former commander of U.S. Forces Korea.

North Korea has fired several land-based missiles this year, including one that flew at least 620 miles high last month. Submarine-launched ballistic missiles are particularly worrisome because they would be harder to detect in advance.

Saturday’s missile test capped a week in which the U.S. slapped sanctions on North Korean leader Kim Jong Un and other top officials for alleged human rights abuses. The North responded by calling the move a “declaration of war” and promising to take “all necessary countermeasures.”

THAAD, which is built by Lockheed Martin Corp., is designed to shoot down short- and medium-range ballistic missiles by intercepting them high in the atmosphere or above it, providing a higher layer of defense that complements lower-tier Patriot missiles. The United States already has a THAAD system stationed in Guam.

Reuters reported that each system costs about $800 million, which could fuel the debate over the cost of maintaining the U.S. military presence in South Korea. That has become an issue in the U.S. presidential campaign after the presumptive Republican nominee, Donald Trump, said South Korea and Japan should pay more for their own defense.

South Korea’s Defense Minister Han Min-koo said Sunday on TV that THAAD would be able to intercept the missiles being tested by the North, including the SLBM and the midrange, land-based Musudan missiles.

Michael Elleman, a missile defense expert at the London-based International Institute for Strategic Studies and a contributor to the 38 North monitoring project, agreed the system could help South Korea block a substantial number of missiles. But “it cannot provide absolute protection against a nuclear attack from the North” and is likely to prompt Pyongyang to devise countermeasures to limit its impact, he wrote.

South Korea began talks with the U.S. on THAAD after North Korea staged its fourth underground test in January, followed a month later by a long-range rocket launch that sent a satellite into orbit. Seoul had been hesitant because of Chinese objections.

The U.S. and South Korea tried to address those concerns, stressing it is strictly a defense measure focused on North Korea. But China swiftly denounced the decision and lodged a complaint with the U.S. ambassador. Beijing fears the radar system could be used to track its weapons as well.

“This is a purely defensive system that we wouldn’t have to talk about and wouldn’t have to consider if the DPRK had proven, in recent weeks and months, willing to take a different, more peaceful path,” State Department spokesman John Kirby told reporters Friday. DPRK is the acronym for the North’s official name, the Democratic People’s Republic of Korea.

The U.S., South Korea and Japan have been trying to pressure Beijing to use its influence over its traditional ally to stop the North’s nuclear ambitions. China signed onto toughened U.N. sanctions against the isolated nation in March.

Joel Wit, a senior fellow at the U.S.-Korea Institute at Johns Hopkins University, said the deployment of THAAD was likely to widen the gap between the U.S. and China over how to deal with the issue.

“It is essential that Washington and Beijing find cooperative paths forward, or else regional tensions are only likely to increase,” he said in a post on the 38north.org blog.

Catherine Dill, an East Asia specialist at the Middlebury Institute of International Studies at Monterey, Calif., said there could be a spillover effect. An international court is due to rule on Tuesday in a case the Philippines, a U.S. ally, has brought against China’s extensive claims and aggressive buildup in the South China Sea.

“A more militarized North Korea, a more provocative North Korea isn’t in China’s interests either,” Dill said. “But there may be more follow-on effects in the South China Sea.”

She also said the announcement about THAAD and the sanctions against Kim were a blow to hopes for a resumption of talks on ending the North’s nuclear program.

“There are some indications that people at a lower level are at least talking,” she said. “But there’s nothing that persuades North Korea that it should change its current behavior this year.”

A joint working group is close to determining the best location for THAAD, balancing the need to ensure the system’s effectiveness with environmental, health and safety concerns. Several Korean cities already have seen protests with residents demanding that the system not be placed in their midst.

The defense minister said the site should be announced soon, but the specific location will be kept secret for security reasons.

The divided peninsula technically remains at war after the 1950-53 conflict ended with an armistice instead of a peace treaty. The U.S. has about 28,500 servicemembers stationed in South Korea.

Stars and Stripes staffer Yoo Kyong Chang contributed to this report.

gamel.kim@stripes.com

Twitter: @kimgamel