WASHINGTON (Reuters) - The U.S. Navy’s Third Fleet will send more ships to East Asia to operate outside its normal theater alongside the Japan-based Seventh Fleet, a U.S. official said on Tuesday, a move that comes at a time of heightened tensions with China.

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The Third Fleet’s Pacific Surface Action Group, which includes the guided-missile destroyers USS Spruance and USS Momsen, was deployed to East Asia in April.

More Third Fleet vessels will be deployed in the region in the future, said a U.S. official who requested anonymity. He and a second official said the vessels would conduct a range of operations, but gave no details.

China claims most of the South China Sea, through which $5 trillion in ship-borne trade passes every year. The Philippines, Vietnam, Malaysia, Taiwan and Brunei have overlapping claims, as well as close military ties with the United States.

China has been angered by what it views as provocative U.S. military patrols close to islands that China controls in the South China Sea. The United States says the patrols are to protect freedom of navigation.

On Wednesday, a spokesman for China’s Foreign Ministry said if U.S. actions had a destructive impact on regional peace and stability and the interests of countries in the region, then China would “definitely be opposed and concerned”.

“How the U.S. military uses its taxpayers’ dollars to carry out deployments is its own affair,” ministry spokesman Lu Kang told a regular briefing. “I’m not concerned about it. What I’m concerned about is regional peace, security and stability.”

The Third Fleet, based in San Diego, California, traditionally has confined its operations to the eastern side of the Pacific Ocean’s international dateline.

Japan’s Nikkei Asian Review quoted the commander of the U.S. Pacific Fleet, Admiral Scott Swift, as saying on Tuesday that the move came in the “context of uncertainty and angst in the region,” an apparent reference to China’s behavior.

Swift argued that the Navy should utilize the “total combined power” of the 140,000 sailors, over 200 ships and 1,200 aircraft that make up the Pacific Fleet.

The Seventh Fleet consists of an aircraft carrier strike group, 80 other vessels and 140 aircraft. The Third Fleet has more than 100 vessels, including four aircraft carriers.

Chinese officials have blamed the rising tension on the United States. “I think before Americans’ so-called ‘rebalancing in Asia-Pacific,’ the South China Sea was very quiet, very peaceful,” Liu Xiaoming, China’s ambassador to Britain, told Reuters in an interview last week.

“China was talking to the neighboring countries. We had a Declaration of Conduct. And the Philippines was talking to us. Once the Americans came in, so-called `rebalancing,’ things changed dramatically.””They want to find an excuse to have their strong military presence in the South China Sea and in the Asia Pacific. If it is so quiet, what is the reason for them to be there?” he asked.

Greg Poling, director of Asia Maritime Transparency Initiative at the Center for Strategic and International Studies think tank, said on Tuesday that the move appears to be part of President Barack Obama’s plan to shift 60 percent of U.S. naval assets in Asia as part of his rebalance of resources to the region in the face of China’s rise.