The voice is that of a soft-spoken 28-year-old, but the message is vintage Osama bin Laden, giving orders to kill. When the audio recording began turning up on jihadist websites two weeks ago, it was as if the dead terrorist was channeling himself through his favorite son.

"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.