The navies of South Korea and the United States, along with Japan's Maritime Self-Defense Force, staged trilateral anti-submarine exercises for the first time in five years on Friday, amid tension over North Korea's series of missile tests.

The drills were held in international waters off the Korean Peninsula's east coast, just a day after North Korea fired two ballistic missiles into the sea off its east coast and U.S. Vice President Kamala Harris visited Seoul and the heavily fortified border between the two Koreas.

Thursday's test was the third such launch in five days by Pyongyang, which has fired an unprecedented number of missiles this year.