SEOUL, South Korea — The leaders of South Korea and China moved on Thursday to mend ties that have been strained by the deployment of an American missile-defense system in South Korea.

During a congratulatory call from President Xi Jinping of China to Moon Jae-in, South Korea’s newly minted president, Mr. Moon revealed his plans to send a delegation to Beijing to resolve the dispute over the system, which China views as a threat to its security, Mr. Moon’s office said.

Mr. Xi also asked him to visit Beijing, Mr. Moon’s office said.

Mr. Moon, a liberal, has criticized the system, known as the Terminal High Altitude Area Defense, or Thaad. His conservative predecessor, Park Geun-hye, agreed to its deployment, saying it was needed to protect South Korea from a growing ballistic missile threat from the North.

Thaad is one of the thorniest diplomatic issues the new South Korean leader faces. If he asks the United States to withdraw the defense system, which became operational last week, he risks rupturing South Korea’s close alliance with the United States and looking as if he is succumbing to Chinese pressure.