The largest U.S. military exercise in the Pacific since the Vietnam War ended Friday after demonstrating to North Korea and other nations in the region the United States' ability to "quickly amass" a huge combat force should the need arise, officials said.

The five-day "Valiant Shield" exercises brought together an armada of three aircraft carriers and 25 other ships, along with 22,000 troops and 280 warplanes, off this tiny island in the western Pacific.

But as the maneuvers began, tensions were rising in the region over the possible test-launch of a North Korean long-range missile — prompting two ships participating in the games to be assigned off the Korean coast to monitor the activity.

Though officials stressed the exercises were not held in response to the North Korean activity or directed at any one nation, they said the games were a demonstration of the United States' capabilities should a crisis arise.

"Valiant Shield was a demonstration of the U.S. Pacific Command's ability to quickly amass a force in a joint combat environment and project peace, power and presence in the region," Air Force Lt. Gen. David Deptula told The Associated Press.

Deptula said the situation in North Korea had not impacted the exercises, which ended as scheduled Friday evening off this U.S. territory about halfway between Hawaii and Japan.

But as the exercises concluded, the guided missile cruisers USS Curtis Wilbur and the USS Fitzgerald were deployed off the Korean coast monitoring the situation, Pentagon officials said.

Lt. Cmdr. Mike Brown, a spokesman for the exercises, confirmed the ships, based in Japan, were part of the Valiant Shield armada. But he refused to provide further details or confirm whether they had been diverted from the exercises or were monitoring the situation while continuing their war games' duties.

Along with the three carriers and their strike forces, the maneuvers featured a four-plane squadron of B-2 stealth bombers, and dozens of fighter jets brought in from as far away as New York state.

Altogether, the aircraft flew 1,993 sorties, according to Sr. Master Sgt. Charles Ramey, an Air Force spokesman.

Officials refused to comment on the specific scenarios and tactics used during the games, but said they were intended to boost the ability of the Navy, Air Force and Marines to work together and respond quickly to potential contingencies.

Adm. Gary Roughead, who commands both the U.S. Pacific Fleet and the joint task force directing the Guam exercise, said the recent deployment of an extra aircraft carrier — the USS Abraham Lincoln — to the Western Pacific enabled the exercise to take place.

"We were able to do this because of the increased focus and the importance that people are placing on the Pacific," Roughead said Thursday at his Pearl Harbor headquarters as the drills entered their final hours.

North Korea, meanwhile, once again proved to be the region's wild card.

Officials in the United States, South Korea and Japan say they believe North Korea may be ready to test launch a Taepodong 2 long-range ballistic missile at any time. The missile is believed be able to reach parts of the western United States.

Pyongyang shocked Tokyo by launching a Taepodong that flew over Japan's main island in 1998. North Korea claimed the launch successfully placed satellite in orbit, but that claim has been widely disputed.

North Korean leader Kim Jong-il agreed on a moratorium on long-range missile launches during a summit with Japanese Prime Minister Junichiro Koizumi in 1999. Pyongyang has honored that agreement, and Tokyo has threatened to impose sanctions if it goes through with the launch this time.

For the first time, the exercises were opened to a 10-member delegation of top Chinese military officers.

Military relations between Beijing and Washington cooled when an American spy plane was captured in 2001, and the Pentagon has recently criticized Beijing's secrecy and its double-digit military budget increases.

Anti-submarine warfare was a major focus of the games, reflecting growing concerns over China's rapidly improving submarine fleet.

Still, senior U.S. military officials said that are cautiously trying to mend the rift with Beijing through person-to-person engagement.

Adm. William J. Fallon, the top U.S. commander in the Pacific, said before the exercises began that implicit in the invitation for the Chinese to observe the exercises was the expectation that China would reciprocate.

"I think that would be the logical step," said Capt. Terry Kraft, who showed the delegation around the USS Ronald Reagan aircraft carrier. "We showed them everything we do from top to bottom. We gave them a very good, transparent look at how we do operations out here."