"You gave us every legitimacy and every opportunity to continue fighting you," al-Zawahri said, addressing the U.S. in the video aired by CNN, which appeared to be new. "You should worry about your presence in the (Persian) Gulf and the second place you should worry about is Israel."
The bespectacled Al-Zawahiri was dressed in white and seated in front of a wall of bookshelves.
"Your leaders are hiding from you the true extent of the disaster," he said. "And the days are pregnant and giving birth to new events, with Allah's permission and guidance."
The video could not be located by The Associated Press on any militant Web sites that normally carry messages and videos from Al-Zawahiri and other Al Qaeda figures. As-Sahab, the terror network's media arm, posted notices late Sunday that the video would be posted shortly.
It was unclear where CNN got the video. The network quoted a counterterrorism expert as saying the video had appeared on the Web site for As-Sahab, but the production company normally uses other Islamic Web sites to post its material.
The video appeared to be new. In it, Al-Zawahiri refers to Israel's bombardment of Lebanon this summer and the capture of Israeli soldiers by Hezbollah and militants in Gaza.
The SITE Institute, an organization that monitors militant Web sites, said it too obtained a copy of the one-hour, 16 minute video entitled "Hot Issues."