BEIJING — After more than a year of frosty relations bordering on hostile, South Korea’s leader, Moon Jae-in, pledged a “new start” on Thursday in his country’s dealings with China as he met with President Xi Jinping, a re-engagement that China hopes will lead to stepped-up diplomacy on disarming North Korea.

The two leaders moved to repair ties that had soured over China’s anger at the deployment of an American antimissile system on South Korean soil. China fears the antimissile system, meant as protection against North Korea, threatens its own security.

Anxious to improve relations with the liberal-leaning Mr. Moon, China moved to settle the dispute over the antimissile system in late October, and began to ease the unofficial trade war it had launched against Korean cars and consumer goods.

But Beijing argues that the agreement was only “provisional,” and is pushing for the eventual removal of the system, the Terminal High Altitude Area Defense, or Thaad.