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.