(CNN) North Korea may be preparing to test engines and other components of its missile program, an administration official tells CNN, but senior military commanders said Friday that the US is ready for "whatever" Pyongyang might do.

Administration officials are closely 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 several 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.

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.

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 Friday that the Pentagon does not "discuss any intelligence or indicators" on what the US may be seeing in the way of preparations by North Korea.

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