The U.S. and China have held “very frank” discussions about North Korea and the possibility that the country will soon conduct a nuclear test this week, according to top Washington officials on Thursday.

National Security Advisor Jake Sullivan said he broached the issue of a DPRK nuclear test with his Chinese counterpart Yang Jiechi in Luxembourg earlier this week.

“On North Korea, we have expressed our concern that North Korea is preparing to conduct another nuclear test. We have said that publicly, we have communicated that to China,” Sullivan said, speaking at a national security conference meeting hostedby