U.S. Navy Aircraft carriers USS John C. Stennis, front, and USS George Washington sail in formation with an escort vessel during a training exercise in waters near Guam, earlier this month.

TOKYO – It’s probably just a coincidence; no need to worry yet. But the U.S. has quietly assembled a powerful air, land and sea armada not far from where Japan and China are squaring off over disputed islands in the East China Sea.

Two Navy aircraft carrier battle groups and a Marine Corps air-ground task force have begun operating in the Western Pacific, within easy reach of the Senkaku Islands. That’s where Japanese and Chinese patrol boats are engaged in an increasingly tense standoff.

Chinese vessels have repeatedly entered territorial waters around the small islands in recent weeks and Coast Guard vessels from Japan and Taiwan fired water cannons at each other last week. The islands are controlled and administered by Japan, but claimed by both China and Taiwan.

No warships have been directly involved in the confrontations, so far. But China has vowed to continue sending patrol vessels into territorial waters and Japan has assembled scores of Coast Guard vessels to “defend” the islands.

The U.S. hasn’t taken sides in the ownership dispute, and Secretary of State Hillary Clinton has called for “cooler heads” to prevail. Nonetheless, U.S. officials have stated clearly that the Senkakus fall under the U.S.-Japan security treaty, which would require the U.S. to come to Japan’s aid in case of attack.

Navy officials confirmed Sunday that the USS George Washington carrier strike group has begun operating in the East China Sea, near the disputed islands. The USS John C. Stennis group is only slightly further away in the South China Sea. Each carrier is armed with more than 80 warplanes, and strike groups typically include guided-missile cruisers and destroyers, submarines and supply ships.

In the nearby Philippine Sea, some 2,200 Marines are embarked aboard the USS Bonhomme Richard and two escorts. The Marines are equipped with amphibious assault vehicles, light armored vehicles, artillery, helicopters and Harrier fighter jets.

Carrier groups and Marine task forces often operate alone, so the convergence of the three groups in a relatively small part of the Pacific represents an unusual concentration of firepower. All three are fresh from training exercises in and around Guam. Those exercises included live-fire with missiles and joint beach landings by U.S. Marines and Japanese ground troops.

A spokesman for the U.S. Pacific Command says the training missions and carrier deployments are not necessarily related to the Senkaku tensions. The islands are called Diaoyu in China, and Tiaoyutai in Taiwan.

“These operations are not tied to any specific event,” said Capt. Darryn James, a spokesman for the U.S. Pacific Command in Honolulu. “As part of the U.S. commitment to regional security, two of the Navy’s 11 global force carrier strike groups are operating in the Western Pacific to help safeguard stability and peace.”

In truth, the carrier and Marine deployments may have as much to do with the “re-balancing” of U.S. forces in the Asia-Pacific region, and with an unrelated crisis in the Middle East, as with the squabble in the East China Sea.

The George Washington battle group and the Marine task force, both based in Japan, were scheduled to conduct separate but overlapping exercises in the Guam region well before the Senkaku dispute heated up. Guam and nearby Tinian Island have been tabbed as a hub for the “re-balancing” of U.S. forces in the region — a hedge against China’s growing military power and ambitions in the region.

The Stennis is being sent from its homeport in Washington state to the Persian Gulf, four months ahead of schedule in response to the escalating crisis over Iran’s nuclear program. The Guam exercises allowed the Stennis to grab a few days of extra training with the George Washington group en route. The Senkakus are situated close to the major sea routes from Pacific to Mideast; it is unclear if the Stennis group is simply passing, by or will remain awhile.

The Marines, meanwhile, were expected to move from Guam to the Philippines for previously scheduled training with the Philippines military.

Navy spokesman James said he could not comment on future ship movements.

Although significant oil and gas deposits may exist within the islands’ territorial waters or exclusive economic zone, the Senkaku dispute has centered largely on old grievances and resurgent nationalism. U.S. officials have privately expressed frustration with the lack of diplomatic progress in resolving the dispute. China placed two-page ads in major U.S. newspapers this weekend, accusing Japan of “stealing” the islands and citing claims that date back hundreds of years.

The Senkakus are located about 100 miles (160 km) northeast of Taiwan and about 200 miles (320 km) east of the Chinese mainland.

While the big U.S. fleet might have been intended as a warning to China not to escalate the islands dispute, it may have been intended to focus Japan’s attention, as well.

Or, it could have been a coincidence.