The CFC has served as a command structure for the joint operation of military forces of the two allies since the 1950-53 Korean War. Seoul handed over control to the US shortly after the start of the war.

As the Obama administration gradually implements its Asia-Pacific strategy, the US armed forces are considering a return to some bases in Southeast Asia to extend its reach in the region.

The Pentagon has intensified discussions with Thailand about creating a regional disaster relief hub at an American-built airfield that housed B-52 bombers during the 1960s and 1970s.

In June, Panetta also visited Vietnam's naval and air base at Cam Ranh Bay, making him the highest-ranking US military official to do so since the end of the Vietnam War. The defense minister hailed the promising prospect of US ships again becoming a common sight at the deep-water port.

The US armed forces are also seeking a greater presence in the Philippines, including at the Subic Bay naval base and the former Clark Air Base, once the largest US military installation in Asia, as well as a key repair and supply hub during the Vietnam War.

Washington has been forging closer military ties with countries in the region and has announced that 60 percent of the US Navy's fleet will be based in the Asia-Pacific by 2020, up from less than 55 percent at present.

Currently, the US fleet is almost evenly split between the Atlantic and Pacific oceans.

Meanwhile, the Pentagon has sped up moves to reshuffle the military chiefs in charge of the region, as General Herbert Carlisle officially took office on Friday as the new commander of the US Command of Pacific Air Forces.

The command includes units in Alaska, Guam, Hawaii, Japan and the ROK. Carlisle's new job came just months after US Navy four-star admiral Samuel Locklear was appointed as Commander of US Pacific Command in March.

Experts said joint military drills and enhanced security cooperation has become Washington's favored way to boost military presence, and since the start of the year, US armed forces have increasingly engaged in joint military exercises in the Asia-Pacific region.

The Rim of the Pacific Drills 2012, led by Washington and held in Hawaii and surrounding maritime areas, involved 22 countries and wrapped up on Friday.

US warships and fighter jets have also participated in almost 20 war games in the Asia-Pacific over the past seven months, more than half of all war games conducted in the area in that period, Xinhua News Agency reported.

US Deputy Defense Secretary Ashton Carter traveled to Thailand in late July, and praised the multilateral military exercise between the two countries known as Cobra Gold. The annual exercise began in 1980 and Carter said has been "key to enhancing cooperation in the region".

Economic factors

Analysts said economic and financial factors are behind Washington's recent series of moves stressing security cooperation and rebuilding mutual trust with countries in the region.

Zhang Junshe, deputy director of the Naval Military Studies Research Institute, said enhancing military alliances is a must for the Obama administration, which has been troubled by financial problems.

"The US has not entirely recovered from the global economic downturn, and its increasing calls to involve alliances are aimed at sharing the burden," Zhang said.

Washington's dependence on military alliances is mounting, and some US politicians have even asked countries like Australia to increase their defense budget to "pay the bill", Zhang Junshe also warned.

The return of the US armed forces to the region is not just "a matter of power", but also serves the profit of US trades, analysts said.

Zhu Feng, a professor of international relations at Peking University, said Washington is considering its return to Asia in the economic sphere.

The Trans-Pacific Partnership Agreement, a major trade framework campaigned by Washington, "serves as an economic basis for stabilizing and enhancing the US' strategic presence in the region", Zhu said in an article in the Beijing-based Contemporary International Relations magazine in April.

Meanwhile, Washington is also facing challenges in the region.

In Japan, around 200 locals gathered on Aug 5 in Iwakuni city to protest the deployment of the Osprey aircraft, Kyodo reported.

Xinhua also warned that the notable increase of US military presence in the region has sent a dangerously wrong message to some countries and thus "undermines the region's peace and stability".

Despite the record number of participating countries in the Pacific joint drill, some of the countries do not intend to contain China and they refuse to take sides between China and the US, Zhang added.

Australia also remains cautious of the Pentagon's shifting of might back to the region. Australian Defense Minister Stephen Smith said on Thursday that while negotiations were under way to increase US navy access to Australia's Indian Ocean base, HMAS Stirling, it would never become a US military base.

"We have made it crystal clear from the first moment - we don't have United States military bases in Australia. We don't see the need for that," Smith told Australian Broadcasting Corp television.

Australia on Thursday also rejected a proposal by a Washington-based think tank to base a nuclear aircraft carrier strike group on Australia's west coast.

A Pentagon-commissioned report by the Center for Strategic and International Studies on repositioning US forces in the region suggested relocating an aircraft carrier from the US East Coast to an Australian naval base south of the city of Perth.

The Australian base would give the US a second carrier strike group in the Asia-Pacific region, the first with an existing Japanese home port in Yokosuka.

Hugh White, head of Australian National University's Strategic and Defense Studies Center, said American combat troops had not been based in Australia since World War II and that was unlikely to change in the future.

"There's a concern that the more the US builds up its military posture in the Western Pacific as part of President Barack Obama's pivot to Asia, the higher the risk that the US-China relationship will become more competitive, more adversarial, more hostile," White told The Associated Press.

White warned such move "pushes Australia close to the point of having to make a choice between the US and China, and that's something we badly want to avoid".

The Associated Press contributed to this story.

zhangyunbi@chinadaily.com.cn