Washington (CNN) Former national security adviser John Bolton has issued his sharpest rebuke of the White House's approach to North Korea's nuclear ambitions in a new interview with Axios published Sunday, asserting that "the idea that we are somehow exerting maximum pressure on North Korea is just unfortunately not true."

His comments come as North Korea may be preparing to test engines and other components of its missile program, an administration official tells CNN.

Bolton told Axios he does not think the White House "really means it" when President Donald Trump pledges to halt the hermit nation from nuclear weapon development or "it would be pursuing a different course."

"We're now nearly three years into the administration with no visible progress toward getting North Korea to make the strategic decision to stop pursuing deliverable nuclear weapons," he told the news outlet.

Administration officials are monitoring satellite imagery for signs that North Korea may soon conduct a new round of weapons testing to deliver the "Christmas gift" that Pyongyang's officials have promised the US if it doesn't ease up on sanctions.

Read More