US President Donald Trump (R) and DPRK Chairman Kim Jong-un at a private meeting during the second DPRK-US summit in Hanoi on February 28, 2019. (Photo: AFP/VNA)

Bolton made the comment in an interview with FOX News on Thursday after a US research group reported that satellite imagery indicates North Korea is rebuilding its missile facilities.

Bolton said if the report turns out to be correct, he will be very disappointed, echoing comments Trump made the previous day.

Bolton said the President is obviously open to talking again, but didn't say when or where.

South Korean News Agency Yonhap on Tuesday reported that the Korean National Intelligence Service (NIS) had detected signs that North Korea is restoring part of the Dongchang-ri missile launch site it tore down after the first summit with US President Donald Trump last June.