“Prepare diligently to inflict crippling losses on those who have disbelieved,” Hamza bin Laden, scion of the Sept. 11, 2001, mastermind, says in a thin baritone that eerily echoes his father. “Follow in the footsteps of martyrdom-seekers before you.”

The recording, first aired May 13, is one in a string of recent pronouncements by the man who many terrorism experts regard as the crown prince of al-Qaeda’s global network. Posted just two weeks before Monday’s suicide bombing in Manchester, England, the message includes a specific call for attacks on European and North American cities to avenge the deaths of Syrian children killed in airstrikes.

The recording provides fresh evidence of ominous changes underway within the embattled organization that declared war against the West nearly two decades ago, according to U.S., European and Middle Eastern intelligence officials and terrorism experts. Decimated by U.S. military strikes and overshadowed for years by its terrorist rival, the Islamic State, al-Qaeda appears to be signaling the start of a violent new chapter in the group’s history, led by a new bin Laden — one who has vowed to seek revenge for his father’s death.