SHANGHAI (Reuters) - China's top admiral said his forces have shown "enormous restraint" in the face of U.S. provocations in the South China Sea, while warning they stand ready to respond to repeated breaches of Chinese sovereignty.

Beijing, which claims almost the entire energy-rich South China Sea through which $5 trillion in ship-borne trade passes yearly, has stepped up a program of land reclamation and construction in disputed islands and reefs there that has sparked concern in the Asia-Pacific region.

The United States has called for a halt to China's artificial island building, and in recent weeks has tried to signal its determination to challenge Beijing over the disputed sea by sending military ships and planes near the islands.

"The Chinese navy has closely monitored the provocative actions of the United States and issued several warnings, while exercising enormous restraint in the interests of safeguarding the overall situation in bilateral relations," said Wu Shengli, commander of the People's Liberation Army Navy, according to a report on the defense ministry's website late on Thursday.

"If the United States carries out repeated provocations despite China's opposition, we have the ability to defend our national sovereignty and security."

Wu made the comments in a meeting in Beijing on Thursday with Admiral Scott Swift, commander of the United States' Pacific fleet, the report said.

Vietnam, the Philippines, Taiwan, Malaysia and Brunei also claim parts of the South China Sea.

China's Defence Ministry said on Friday that the navy had recently carried out anti-submarine drills in the South China Sea, with submarines, warships and ship-born helicopters.

State television showed warships conducting live-fire drills and troops deploying from amphibious vehicles on to beaches.

It did not say when the exercises happened, nor where exactly. Such drills are not uncommon.

In the Philippines on Wednesday, U.S. President Barack Obama said China must stop the land reclamation.

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Obama planned to raise the South China Sea dispute at another summit this weekend in Malaysia, his main Asia policy adviser Daniel Kritenbrink said.

Swift was in Shanghai earlier this week where the USS Stethem, an Arleigh-Burke class destroyer, made a port call.

It was the third visit first to China by a U.S. navy vessel this year and the first since a similar guided missile destroyer, the USS Lassen, angered Beijing by sailing near one of China's man-made islands late last month to challenge the 12-nautical-mile territorial limits China claims around the artificial islands.

(Reporting by John Ruwitch; Additional reporting by Ben Blanchard and Michael Martina in Beijing; Editing by Stephen Coates and Sanjeev Miglani)