Pope Francis says the detonation of atomic bombs at Hiroshima and Nagasaki 70 years ago remains "a permanent warning to humanity" to reject war and ban weapons of mass destruction.

The pope during his traditional Sunday blessing recalled the U.S. detonation of atomic weapons as "a tragic event that still arouses horror and revulsion." He said the bombings of the Japanese cities had become a symbol of mankind's destructive power when science and technology are put to "distorted use."

U.S. planes dropped two atomic bombs on two days in August 1945, unleashing unprecedented destruction that killed more than 200,000 people and left survivors with lifelong psychological and physical scars. It was the first and only time nuclear weapons have been used.