He stressed that efforts to dismantle North Korea's nuclear weapons program are "diplomatically-led" with military options as a back-up.

"The State Department is working very hard to exercise those diplomatic options and initiatives and efforts with China," Manning said when asked if China, North Korea's main ally and economic benefactor, can still be trusted.

North Korea has come under growing pressure and sanctions to abandon its pursuit of nuclear-tipped missiles, which it says are aimed only at deterring US hostility.

The communist regime tested its first long-range missiles capable of reaching the US mainland in July, followed by its sixth and largest nuclear test in September.

Since mid-September, it has not conducted any provocations, triggering speculation as to what the regime could do next or whether there could be an opening for dialogue between Washington and Pyongyang.

In a phone call earlier in the day, US President Donald Trump and his French counterpart, Emmanuel Macron, "agreed on the need for all nations to impose and maintain maximum pressure on the North Korean regime to denuclearize," the White House said. (Yonhap)