The United States will deploy a sophisticated anti-missile defense system to Guam in response to North Korean threats to U.S. military bases in the Pacific, the Pentagon said Wednesday.

The Terminal High Altitude Area Defense system (THAAD) is a land-based system designed to destroy incoming short-, medium- and intermediate-range missiles by crashing into them in the air. Only two batteries of the system, produced by Lockheed Martin, are currently deployed, both at Fort Bliss, Tex.

A Pentagon statement said the system should arrive in Guam “in the coming weeks as a precautionary move to strengthen our regional defense posture against the North Korean regional ballistic missile threat.”

The announcement followed North Korea’s banning of South Korean workers from entering a joint industrial complex near the demilitarized zone. Obama administration officials had said earlier that the move would signal a more serious crisis beyond the bellicose rhetoric issued by North Korea over the past several weeks.

The dispatch of the THAAD system — the military’s first operational deployment of the relatively new system — marked another significant escalation in the threat and response cycle between the United States and North Korea. It was matched by a new warning, attributed by the North’s state news agency to a military spokesman, that North Korea had “ratified” plans for a “merciless” nuclear operation against the United States.

Until this week, senior administration officials appeared to play down the risk of military engagement as familiar North Korean rhetoric, while saying the United States was fully prepared to defend itself and its allies in South Korea and Japan. Secretary of State John F. Kerry is due to visit both countries next week.

But on Wednesday, Defense Secretary Chuck Hagel called the North Korean actions a “real and clear danger and threat” to the United States and its allies in the region. “They have nuclear capacity now. They have missile delivery capacity now,” Hagel said in a speech at the National Defense University in Washington.

Hagel specifically cited “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.

Earlier this week, the North announced it would restart a nuclear reactor, shuttered in 2007, that is capable of producing plutonium for nuclear weapons, and declared a “state of war” in the Korean Peninsula.

The current cycle began with North Korea’s long-range rocket launch in December and underground nuclear test in February, provoking tighter U.N. sanctions and the deployment of U.S. nuclear-capable stealth bombers to the peninsula as part of military exercises with South Korea.

Last month, Hagel said the military would increase the number of ground-based interceptors in Alaska over the next three years to counter the threat of long-range North Korean missiles.

The Pentagon announcement Wednesday did not specify where the THAAD batteries destined for Guam are currently based. “Though we do have a limited number of THAAD units available for deployment, we are quite confident in our ability to rapidly redeploy this system as dictated by threat levels,” said Defense Department spokeswoman Lt. Col. Monica Matoush.

The THAAD missile has an estimated range of 120 miles and was designed as one element in an integrated defense system that includes the Aegis missile for long-range threats and the short-range Patriot missile. The Pentagon said earlier this week that it has moved two Aegis-class warships to the Pacific.

The standard THAAD configuration includes six launchers, each with multiple interceptors. The first battery was activated at Fort Bliss in 2008, where operating teams trained for its use, and operational tests have included launches at the Pacific Missile Range Facility in Kauai, Hawaii.

Pentagon officials indicated that one of the units will probably come from Fort Bliss, speeding up a permanent move to Guam that had been planned for some time in the future.

Then-Defense Secretary Robert M. Gates announced the temporary deployment of a THAAD battery to Hawaii during an earlier set-to with North Korea, in June 2009, when the missile defense system was still in a testing phase. The battery was later returned to Fort Bliss.

In addition to the two existing batteries, the Pentagon agreed to sell two THAAD batteries to the United Arab Emirates as part of a $16 billion package of U.S. defense equipment to the UAE and Qatar designed to boost Persian Gulf defenses against the threat from Iran.

Anne Gearan contributed to this report.