WASHINGTON — A U.S. Navy submarine began leaking water with trace amounts of radioactivity during a port call in late March in Sasebo, Nagasaki Prefecture, U.S. Navy officials said Friday.

The leak was found on the USS Houston, a Los Angeles-class fast attack submarine, after it went to Hawaii for routine maintenance last month, the officials said, confirming a CNN television report earlier.

The officials said the amount of radiation leaked into the water was very low, but the Navy alerted the Japanese government on Friday (Japan time) because the submarine had docked in Sasebo during its travels around the Pacific.