U.S. special envoy for North Korea Sung Kim has conveyed his concerns to his Chinese counterpart Liu Xiaoming over the "unprecedented number" of ballistic missile tests by North Korea this year and emphasized the need to fully enforce sanctions on Pyongyang, the State Department said Thursday.

U.S. special representative for North Korea Sung Kim. (Kyodo)

The concerns were expressed during a video conference on Wednesday intended to discuss North Korea's "increasingly destabilizing and escalatory behavior," the department said in a press release.

The talks are the latest exchanges between senior officials of the United States and China, after President Joe Biden and President Xi Jinping met on the sidelines of a summit of the Group of 20 major economies in Indonesia in an effort to manage their intensifying rivalry and maintain open lines of communication.

Kim strongly condemned North Korea's missile launches, which have included intercontinental ballistic missiles, saying that they violate U.N. Security Council resolutions aimed at curbing the country's nuclear and missile programs.

The special representative for North Korea also stressed the need for "all U.N. member States to fulfill their obligations" in implementing the sanctions, the State Department said.

But he also reaffirmed that the United States is committed to diplomacy and is prepared to meet with North Korea "at any time" for talks toward denuclearization.

In addition to conducting a barrage of ballistic missile tests this year, North Korea is feared to be preparing to carry out what would be its first nuclear test since September 2017 and seventh overall.