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By Jim Miklaszewski

U.S. defense officials said Saturday that they have no reliable information to confirm North Korea's latest boast — that it has successfully tested a new long-range rocket engine capable of targeting America with nuclear strikes.

While U.S. military and intelligence officials acknowledge the isolated nation is aggressively pursuing miniaturized nuclear warheads and long-range ballistic missiles, they remain skeptical of North Korea's claim, announced by North Korea's official Korean Central News Agency.

Related: North Korea Launches 15th 'Projectile' in 2 Weeks

North Korea has already launched two medium-stage ballistic missiles that put two satellites into uncontrolled orbit in space, but officials contend that's well short of being able to attack the U.S. with a nuclear weapon.

U.S. officials have said that at the current rate of testing, North Korea could ultimately achieve its goal.

In response to the potential threat, the U.S. has stationed 30 anti-ballistic interceptor missiles in Alaska and at Vandenberg Air Force Base in California.

The system is designed specifically to defend against a small-scale nuclear attack from a rogue nation by intercepting and destroying an incoming ballistic missile while it is still in space.