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.