The Pentagon has placed its national missile defense shield on heightened alert amid reports that North Korea is preparing a missile flight test, according to defense officials.

The higher alert status includes moving two Aegis-equipped missile defense ships to waters near North Korea and readying long-range ground-based interceptors in Alaska and California, said officials familiar with the status.

The Pentagon also announced on Wednesday it is deploying one of its newest ground-based missile defenses to the U.S. island of Guam, a major U.S. military hub in the South Pacific.

The Terminal High-Altitude Area Defense system (THAAD) will be sent to Guam in the coming weeks "to strengthen the regional defense posture against the North Korean regional ballistic missile threat," a Pentagon statement said.

The increased readiness of the missile shield followed harsh threats by the communist regime in North Korea to conduct nuclear missile attacks against the United States.

Defense Secretary Chuck Hagel said following a speech yesterday that North Korea has a "nuclear capacity now," along with missiles.

Hagel said Pyongyang recently stepped up bellicose and dangerous rhetoric "and some of the actions they've taken over the last few weeks present a real and clear danger and threat to the interests, certainly, of our allies, starting with South Korea and Japan, and also the threats that the North Koreans have leveled directly at the United States regarding our base in Guam, threatened Hawaii, threatened the West Coast of the United States."

"We have to take those threats seriously," he said. "I think we have had measured, responsible, serious responses to those threats."

The Pentagon flew B-52 strategic bombers and then B-2 nuclear bombers near North Korea in a sign of U.S. "extended deterrence" nuclear protection during recent joint exercises with the South Korean military.

Pyongyang announced on March 30 that relations with the South had entered a "state of war." The notice was made for the first time in an unusual "special statement" reflecting the government, ruling communist party, and other organizations.

It was the first time the regime had used the term "state of war" to describe relations with the South and highlighted the North’s nullification of the armistice agreement ending the Korean War.

A U.S. official said there have been some small-scale military maneuvers underway in North Korea.

The official said North Korea used military exercises as cover for dispatching a submarine that covertly sank the South Korean warship Cheonan in 2010, killing 46 sailors on board.

The missile shield activation also follows intelligence reports indicating the North’s military recently began moving some mobile missiles around the country, the officials said.

Specifically, officials said the North Koreans appear to be planning to conduct a test flight of a Musudan intermediate-range ballistic missile, a relatively new road-mobile system.

It is the third time since the beginning of the year that intelligence agencies reported a North Korea Musudan flight test could take place.

Officials said there were no signs the North Koreans planned to test fire their new longer-range KN-08 road-mobile intercontinental ballistic missile.

Rep. Mike Rogers (R., Ala.), chairman of the House Armed Services subcommittee on strategic forces, said the United States "must take all reasonable actions in the face of the growing nuclear and missile threats from the unstable regime in North Korea."

"A robust missile defense system is a key element to our overall national security, and I stand ready to work with the administration to ensure we have all of the tools we need," Rogers told the Free Beacon.

The missile defense system includes 30 long-range interceptors based in Fort Greely, Alaska, and Vandenberg Air Force Base. Early warning radar used to detect launches and track enemy missiles are located at Beale Air Force Base, located north of Sacramento, California, and the remote Pacific island of Shemya at the tip of Alaska’s Aleutian Islands.

Additionally, the military operates a transportable high-powered X-band radar in northern Japan that is capable of tracking missile launches and guiding interceptors to their stages or warheads.

The huge, platform based Sea-Based X-Band Radar is now based in waters near Japan and undergoing sea trials and system checks, officials said, and could be employed as part of the missile shield.

The Pentagon announced earlier this week that it had deployed two destroyers equipped with anti-missile interceptors, the USS McCain and the USS Decatur, to waters near the Korean peninsula as part of its beefed up missile defenses against North Korean threats.

George Little, a Pentagon spokesman, declined to say on Tuesday if there were signs North Korea planned to conduct a missile flight tests, citing a policy of not discussing intelligence matters.

Little said, "We can’t rule out the possibility, obviously, that they may conduct some kind of tests or engage in some kind of provocative behavior that would cause problems," adding the United States hopes that does not happen.

It could not be learned how many missile defense ships are now in the region. The Navy is believed to be operating at least four Aegis-equipped warships near North Korea that are equipped with SM-3 anti-missile interceptors. The SM-3 is a very capable missile that can knock down most medium-range missiles. The ships’ Aegis battle management system is built around a high-powered phased-array radar that is capable of tracking missiles hundreds of miles from the ships, as well as objects in space.

The SM-3s provide protection from missile attacks for areas in Northeast Asia, while the ground-based interceptors in California and Alaska can protect the continental United States and Hawaii from attack.

A classified 2009 State Department cable stated that the Musudan intermediate-range missile is based on Russia’s SS-N-6 submarine-launched missile that has a range of up to 2,400 miles.

The missile is fueled by an advanced liquid propellant that is easier to store in missiles than fuel used in other North Korean long-range rockets.

The fuel allows for longer-range missiles and greater warhead capacity on short-range systems.

Additionally, North Korea announced it was closing off South Korean workers from the joint North-South industrial center at Kaesong, located inside near the heavily fortified demilitarized zone separating the two countries.