South Korea has said the possible operation of a controversial American-made missile shield is "not negotiable,” pushing back at China’s efforts to hold President Yoon Suk Yeol to his predecessor’s pledge to freeze its deployment.

Decisions on the deployment of Lockheed Martin Corp.’s Terminal High-Altitude Area Defense system was a matter of South Korea’s self-defense, a senior presidential official told reporters Thursday in Seoul. The Yoon administration is accelerating efforts to "normalize” the operation of the U.S. base in the southern city of Seongju that deployed the THAAD system, the official said.

China is pushing to reaffirm former South Korean President Moon Jae-in administration’s policy of not allowing additional THAAD deployments. The Moon administration made the announcement in 2017 as it aimed to resolve Chinese trade curbs imposed after the first missile-defense system was delivered as part of U.S.-led efforts to counter North Korea’s nuclear expansion.