TOKYO (Reuters) - The U.S. Navy carrier, the USS Ronald Reagan, conducted three days of drills with a Japanese destroyer and two Indian warships in the Sea of Japan, Japan s navy said on Tuesday. The exercise involving five ships, which ended Monday, came amid heightened tension in the region over North Korea s ballistic missile and nuclear tests and as U.S. President Donald Trump began a 12-day tour of Asia beginning in Japan on Sunday.  The exercise helped improve fighting skills and deepened cooperation with India,  Japan s Maritime Self Defence Force said in a press release. The 100,000-ton Reagan, which is based in Japan carries around 70 combat aircraft and is the U.S. Navy s most powerful warship in Asia. The Reagan will join two other carriers in the Western Pacific, the USS Nimitz and USS Theodore Roosevelt, in a potent reminder to Pyongyang of the U.S. ability to rapidly mobilize military force, U.S. officials told Reuters earlier.  