(Adds another U.S. joint exercise with Japan and Australia)
By Sanjeev Miglani
NEW DELHI/TOKYO, July 21 (Reuters) - The United States is conducting two military exercises in Asian waters this week involving allies Japan, Australia and India, the U.S. navy said on Tuesday.
The exercises come as military rivalry between the United States and China is intensifying and days after the United States said China's claims of sovereignty in the disputed South China Sea were illegal.
The United States has long opposed China's expansive territorial claims on the South China Sea, sending warships regularly through the strategic waterway to demonstrate freedom of navigation.
China opposes such exercises and said the U.S. rejection of its claims in the South China Sea raised tension and undermined stability in the region.
The USS Nimitz and the USS Ronald Reagan were deployed to the South China Sea twice this month but this week, the Nimitz was in the Indian Ocean for exercises with the Indian navy, the U.S. navy said, in the latest sign of growing cooperation between the forces.
Rear Admiral Jim Kirk, commander of the Nimitz Carrier Strike Group, said in a statement that Monday's drills with the Indian navy helped improve the interoperability of their forces.
"While operating together, the U.S. and Indian naval forces conducted high-end exercises designed to maximize training and interoperability, including air defense," the U.S. navy said.
India's relations with China have also been strained after a deadly clash on their disputed border in the Himalayas last month, prompting calls in India for closer security ties with the United States and its allies including Japan.
The drills were carried out near India's Andaman and Nicobar islands, off the north end of the Malacca Straits, one of the world's busiest shipping routes for trade and fuel, an Indian source said. India has a military base on the islands.
The U.S. navy said the Nimitz Carrier Strike Group was in the Indian Ocean in support of a free and open Indo-Pacific region.
Separately, the U.S. strike group led by the Ronald Reagan was carrying out drills with naval forces from Japan and Australia in the Philippine Sea, U.S. and Australian officials said on Tuesday.
The exercises are due to end on July 23, Australia's defence department said.
Later this year, the United States will hold naval exercises with India and Japan in the Bay of Bengal and Australia might join.