By Barbara Starr

North Korea likely engaged in a deliberate campaign of deception before a December 12 long-range missile launch, catching the United States and its Asian allies "off guard," according to a U.S. official with direct knowledge of analysis of the incident conducted by U.S. military and intelligence agencies.

The official told CNN that American and Japanese military ships and missile defenses were fully operational and protecting land, sea and airspace on December 12, but that the launch was a surprise when it actually happened.

"We had our dukes up, operationally, but we were caught off guard," the official said.

"The clues point to a concerted effort to deceive us," the official said. The analysis was ordered in the wake of the launch to determine what exactly happened and how much the U.S. intelligence knew at the time.



The official said one conclusion was that while missile defenses can fully protect against a North Korean attack, the North Koreans have shown they can counter U.S. measures to gather intelligence about what they are up to.

"Look, they know when our satellites are passing overhead," the official said. It's believed the North Koreans essentially manipulated the launch so U.S. intelligence satellites simply would not be overhead and able to see what was happening.

The most likely scenario, the official said, was that North Korea wasn't telling the truth when it announced several days before the launch that there were technical problems with the missile.

According to the official, the intelligence analysis found that:

- The United States observed the North Koreans beginning to take apart the three-stage rocket and move parts of it away from the launch pad, then observed what were believed to be so-called replacement parts being moved in.

- In retrospect, those parts appear to have been from a second, older-generation long-range missile that were in storage. Those parts most likely were never used in the December 12 launch.

During this time, when the United States did not have total visibility of the launch site, it's believed the North Koreans either quickly reassembled the original rocket and fired it.

- It's also possible the U.S. miscalculated and the North Koreans never took it apart at all.

Earlier this week, South Korean defense officials warned that the latest North Korean missile had the capability to travel more than 6,000 miles, meaning this type of rocket could strike the United States. However, experts do not believe Pyongyang has a nuclear warhead small enough to fly on the kind of missile.

North Korean officials claimed that the rocket launch succeeded in putting a satellite in orbit.

CNN's Paula Hancocks and Greg Botelho contributed to this report.