South Korea and U.S. Agree to Deploy Missile Defense System

SEOUL, South Korea — South Korea and the United States announced on Friday that they have decided to deploy an advanced American missile defense system in the South, despite strong protests from China, which sees it as a threat to its own security.

The two allies agreed to the deployment of the so-called Terminal High-Altitude Area Defense system, or Thaad, to better protect South Korea and the United States military in the region from North Korea’s growing nuclear and ballistic missile capabilities, a senior Defense Ministry official, Ryu Jae-seung, said at a news conference.

Seoul and Washington have been in talks for months about implementing the new system. Mr. Ryu said that officials from both nations were in the final stage of recommending a site for a Thaad base to their defense chiefs.

In a swift and sharp reaction against the deployment, China’s Foreign Ministry said in a statement that the decision would change the strategic balance in the region and undermine China’s security interests.

“The Chinese side hereby expresses strong dissatisfaction and firm opposition,” the statement said. China’s leader, Xi Jinping, had spent considerable political capital trying to convince President Park Geun-hye of South Korea to reject the push by the Obama administration for the missile system.

The new system was also likely to face resistance from residents in whatever part of South Korea is selected for the base. Villagers and politicians from towns that have been mentioned as possible sites have said they will oppose it, fearing that strong electronic signals from the radar might be harmful to residents’ health, and that their towns would become an early target for North Korean missiles should war break out.

“This is an important R.O.K-U.S. decision,” Gen. Vincent K. Brooks, the top commander of the American military in South Korea, said in a statement, using the acronym for the South’s formal name, the Republic of Korea. “North Korea’s continued development of ballistic missiles and weapons of mass destruction require the alliance to take this prudent, protective measure to bolster our layered and effective missile defense.”

The United States military emphasized that Thaad would “be focused solely on North Korea” and would contribute to a layered system enhancing the alliance’s existing missile defense capabilities against North Korean missile threats.

South Korea agreed to consider the Thaad deployment after the North’s launching of a long-range rocket on Feb. 7, an event widely seen as a cover for developing a long-range ballistic nuclear missile. In March, Washington and Seoul established a task force to discuss a possible deployment.

South Korea’s military has said that Thaad will bolster its defense against North Korean missiles, but its political leaders had been reluctant to commit to it because of China’s objections.

They have expressed fear that the deployment might prompt China to move closer to North Korea as a buffer against the United States and South Korea, and that China might retaliate economically. China is South Korea’s No. 1 trade partner and sends more tourists than any other country.

China is particularly concerned about Thaad in South Korea because its powerful radar could give the United States military the ability to quickly detect and track missiles launched in China, analysts said. The United States military already has a Thaad battery deployed on Guam and operates powerful radar in the region, as well as satellites over China.

While United States policy makers have increasingly worried about North Korea’s efforts to develop a capability to deliver a nuclear warhead on an intercontinental ballistic missile, South Koreans have tended to be less concerned. For decades, they have lived in the shadow of North Korea’s ability to deliver catastrophic destruction: Seoul, the capital, is within the range of thousands of conventional North Korean rockets and artillery pieces.

North Korea had no immediate reaction to the announcement.