U.S. National Security Advisor Jake Sullivan said that the U.S. has conveyed its concerns to China about a possible nuclear test by North Korea.

Sullivan made the remarks on Thursday in a discussion session hosted by the Washington-based think tank Center for a New American Security(CNAS).

Sullivan met with top Chinese diplomat Yang Jiechi, head of the Chinese Community Party's foreign affairs bureau, in Luxembourg on Monday.

Summarizing the meeting, Sullivan said the U.S. expressed its concern that North Korea is preparing to conduct another nuclear test, adding that the U.S. has said that publicly and has communicated that to China.

The top security adviser continued to say that “the proof will be in the pudding” and they will see how things play out.

A U.S. official earlier said that in the meeting with Yang, Sullivan expressed concerns about China's recent veto of a U.S.-drafted UN Security Council resolution aimed at strengthening sanctions against North Korea.