North Korea plans to test a Taepodong 2 missile that is capable of carrying nuclear weapons and reaching the continental United States in the next three weeks, a senior US defense official with access to the latest intelligence told FOX News.

"They appear to be serious. This is no bluff," the U.S. official said. "It could look like an attack on the US, but it won't be." 

The Taepodong 2 was last tested in 2006 and fell shortly after launch. It has never successfully been tested or achieved its maximum range.

The U.S. Navy has put its Aegis radar anti-missile defense system on alert but has stopped short of putting the interceptor missiles on high alert. U.S. intelligence is seeing the North Koreans move the components for a missile launch into place in recent days at a base in North East Korea.

The North Koreans, according to another US analyst, seem to have been emboldened by the world's response - or lack of response - to the recent Iranian satellite launch - and "want to join the club."

Jennifer Griffin currently serves as a national security correspondent for FOX News Channel . She joined FNC in October 1999 as a Jerusalem-based correspondent. You can follow her on Twitter at @JenGriffinFNC.