N. Korea Mocks US Nuclear Flyover, on Track for 20 Nukes

North Korea is mocking the United States for flying two nuclear-capable supersonic bombers over South Korea Tuesday.

It was a show of force to North Korea after the regime's recent nuclear tests.CNN reports the communist regime has called the flyover "bluffing" and "blustering."

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The nuclear warning flyover was also designed to calm rattled nerves in the southern half of the peninsula. South Korea does not have nuclear weapons and relies on the U.S. "nuclear umbrella" for protection.

Some experts warn North Korea will be able to develop the capability to reach the continental U.S. with a nuclear missile within a decade or so. Last week, North Korea conducted its fifth nuclear test, its most powerful to date.

Pyongyang's claim to have used "standardized" warheads in the detonation makes some outsiders worry it is making headway in developing small, sophisticated warheads that can be mounted on missiles that can reach the U.S. mainland.

Nuclear expert Siegfried Hecker, who has regularly visited the North's nuclear facilities, estimates the North may have enough nuclear fuel for about 20 bombs by the end of 2016 and the ability to add about seven new bombs a year.

"Left unchecked, Pyongyang will likely develop the capability to reach the continental United States with a nuclear tipped missile in a decade or so," Siegfried wrote on the North Korea-focused website 38 North.

He said it's more troubling that the recent test successes may give Pyongyang a false sense of confidence.