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(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.

Due to North Korean measures to hide activities at multiple sites, the US cannot be certain what North Korean leader Kim Jong Un may order to be tested, one official said. One scenario suggests a test of a long-range missile or launch of a satellite on a long-range booster.

“Time is on the side of the proliferator,” Bolton told Axios. “The more time there is, the more time there is to develop, test and refine both the nuclear component and the ballistic missile component of the program.”

The Trump administration has been trying to negotiate with North Korea to have it dismantle its nuclear program, which poses a threat to US allies South Korea and Japan, and thousands of US troops based in both countries.

Those talks have been stalled – even as Pyongyang has pursued technical improvements to its program that increasingly could put the US within range of its rockets.

Still, senior military commanders said Friday that the US is ready for “whatever” Pyongyang might do.

When asked about recent comments and indicators from North Korea that Pyongyang may be getting closer to a long-range missile test or some other provocative act, Joint Chiefs Chairman Gen. Mark Milley said that the Pentagon does not “discuss any intelligence or indicators” on what the US may be seeing in the way of preparations.

CNN’s Barbara Starr and Zachary Cohen contributed to this report.