The video, which could not be independently verified, was released by the Islamic State's media arm, according to the IntelCenter, which monitors extremist websites.
Sen. John McCain says a pardon for Jack Johnson would be a message to the world that America is determined to "live up to the noble ideals of freedom, opportunity, and equal justice for all."
Kerry suffered a likely leg injury, but did not lose consciousness, State Department spokesman John Kirby said. The top American diplomat is in stable condition.