BEIJING (Reuters) - China's military said it had recently held intensive anti-submarine exercises in the strategically important South China Sea as part of efforts to hone its capabilities amid rising maritime tensions with its neighbours and their allies.

In an undisclosed area in the South China Sea, more than a dozen flights of anti-submarine patrol aircraft operated non-stop for more than 40 hours searching for submarines and simulating attacks, the Southern Command Theatre of China's People's Liberation Army said in a statement on Monday.

"It has effectively honed the military's round-the-clock aerial anti-submarine combat capabilities," said the statement. The exercise was conducted late at night and in the early morning to accumulate experience at different hours.

The statement did not say whether any non-Chinese submarines were identified in the area.

The United States and its allies have also stepped up military activities, especially in the South China Sea, most of which is claimed by Beijing.

Last week, the U.S. and Indonesian defence chiefs said China's territorial claims in the South China Sea were "inconsistent with international law". The U.S. Navy added that China's "aggressive behaviour" in the area, including the use of water cannons against a Philippine vessel, must be challenged and checked.

The largest of the U.S. Navy's forward-deployed fleets, the Seventh Fleet, headquartered in Japan, operates as many as 70 ships, and has about 150 aircraft and more than 27,000 sailors.

"Japan and the United States have frequent submarine activities in the region," said Chinese military commentator Song Zhongping, but those activities were not disclosed.

(Reporting by Albee Zhang and Ryan Woo. Editing by Gerry Doyle)