The SITE Monitoring Service, which tracks jihadist statements, quoted al-Zawahiri as saying he hoped the protest movements that have overthrown leaders in Egypt, Tunisia and Libya would establish what he called true Islam.
The video was posted on jihadist websites on Monday and titled "The Dawn of Imminent Victory", SITE said.
Al Qaeda, which called for the violent overthrow of secular Arab governments, lost a great deal of relevance as a result of the political upheaval across the Middle East and North Africa.
The video also included a message that al Qaeda said was recorded by Osama bin Laden before his killing in May by U.S. special forces, in which he warns Americans against "falling as slaves" to the control of major corporations.
Ahead of events on Sunday in the United States to commemorate the 10th anniversary of the Sept. 11 attacks, officials had warned of a specific, credible but unconfirmed report of a threat to harm Americans, notably in New York and Washington.
SITE made no mention of any specific threat in its account of the contents of the video.
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