The United States announced Wednesday it is sending an advanced ballistic missile defense system to the western Pacific, as North Korea's military said it received final approval for a nuclear attack.

"The Department of Defense will deploy a Terminal High Altitude Area Defense System (THAAD) Ballistic Missile Defense system to Guam in the coming weeks as a precautionary move to strengthen our regional defense posture against the North Korean regional ballistic missile threat," the Pentagon said in yet another unusual announcement of the deployment of such a strategic weapon.

The move is seen as aimed at discouraging North Korea and assuring Washington's regional allies and American people who have a memory of the Sept. 11 terrorist attack on the mainland.

It comes on the heels of the dispatches of heavy weaponry to Korea for joint drills with the South, including B-52 and B-2 bombers, F-22 stealth fighters, a nuclear-powered submarine and anti-ballistic-missile destroyers.

 "This deployment will strengthen defense capabilities for American citizens in the U.S. Territory of Guam and U.S. forces stationed there," the Pentagon said in a press release.

The THAAD system is a land-based missile defense system that includes a truck-mounted launcher, a complement of interceptor missiles, an advanced tracking radar, and an integrated fire control system.

The Pentagon's announcement almost coincided with North Korea's new statement warning of actual nuclear attack.

The North's military said its "merciless operation" involving a nuclear strike has been approved.

"We formally inform the White House and Pentagon that the ever-escalating U.S. hostile policy toward the DPRK (North Korea) and its reckless nuclear threat will be smashed by the strong will of all the united service personnel and people and cutting-edge smaller, lighter and diversified nuclear strike means of the DPRK and that the merciless operation of its revolutionary armed forces in this regard has been finally examined and ratified," an unnamed spokesman for the General Staff of the Korean People's Army (KPA) told Pyongyang's official news agency, KCNA.

The spokesman cited the Pentagon's deployment of advanced weapons in and near the Korean Peninsula.

 Meanwhile, Secretary of Defense Chuck Hagel described Pyongyang's threats as a "real and clear" danger.

"They have nuclear capacity now, they have missile delivery capacity now," Hagel said, addressing an audience at the National Defense University in Washington. "We take those threats seriously.

We have to take those threats seriously."

 He added, "We are doing everything we can, working with the Chinese, others, to defuse that situation on the peninsula."

 Hagel also met Wednesday with South Korean Foreign Minister Yun Byung-se.

"Secretary Hagel reaffirmed to Minister Yun that the United States' enduring defense and extended deterrence commitments to South Korea will not change and that it is our duty to remain vigilant during this time of heightened tension on the Korean Peninsula," Pentagon press secretary George Little said.

Hagel also pointed out that diplomatic efforts are fundamental to encouraging North Korea to pursue the path of peace, added Little.

Yun is on a visit to Washington main to prepare for a trip here by South Korean President Park Geun-hye in early May. (Yonhap News)