WASHINGTON (Reuters) - Chinese Foreign Minister Wang Yi on Thursday underscored his concerns about the long range of a powerful U.S. radar that could be deployed in South Korea along with an advanced missile defense system and said Washington should explain its plans.

Wang told an event hosted by the Center for International and Strategic Studies think tank that China remained committed to working with the United States and other countries to de-nuclearize the Korean peninsula. He said he was optimistic that the United Nations would agree on a resolution criticizing North Korea for its Jan. 6 nuclear test.

But Wang said China remained concerned that the X-band radar to be deployed with the U.S. Terminal High Altitude Area Defense (THAAD) system built by Lockheed Martin Corp had a range that extended far beyond the Korean peninsula into the interior of China. That in turn, he said, could jeopardize "China's legitimate national security interests."

He said the decision was ultimately up to South Korea, and China understood the desire of the United States and South Korea to ensure the defense of their own countries.

But he said China had raised concerns about the system's capabilities that should be addressed by the United States.

"We believe that China's legitimate security concerns must be taken into account," Wang said. "An explanation must be provided to China."

The United States and South Korea agreed earlier this month to start talks about deploying the THAAD system to South Korea to counter the growing threat of North Korea's weapons capabilities after its Feb. 7 launch of a long-range satellite.

One U.S. defense official said the talks were on track for next week.

(Reporting by Andrea Shalal; Editing by Chizu Nomiyama and Cynthia Osterman)