Air Force Secretary Frank Kendall on Monday warned that China was building up its military to prepare for a potential war with the U.S., and he said America must optimize its forces to counter the rising threat.

Speaking at the Air and Space Forces Association Warfighter Symposium at National Harbor, Md., Kendall said the U.S. must be ready for a “kind of war we have no modern experience with,” though he stressed “war is not inevitable.”

“Our job is to deter that war and to be ready to win if it occurs,” Kendall said. “We’re all talking about the fact that the Air and Space Forces must change, or we could fail to prevent and might even lose a war.”

Kendall said it was vital to prepare for war because China is developing its forces at a rapid pace and has created two new military branches: a force designed to counter aircraft carriers, airfields and other critical assets, and a strategic support service that works to achieve information dominance in the space and cyber domains.

The Air Force secretary said, “China has been reoptimizing its forces for great power competition and to prevail against the U.S. in the Western Pacific for over 20 years.”

“China has been building a military capability specifically designed to achieve their national goals and to do so if opposed by the United States,” he added.

U.S.-China relations have reached a low point amid rising tensions over the self-governing island nation of Taiwan, which Beijing sees as historically part of the mainland.

The U.S. has warned that Chinese President Xi Jinping may seize the island by force if necessary, and President Biden has repeatedly said the U.S. would send troops to help defend the island in such a scenario. Washington maintains informal ties with Taiwan and has provided advanced weaponry to the nation.