Ayman El-Zawahiri said in a video posted on Islamist websites, "ten years have passed since the blessed attacks on New York and Washington and Pennsylvania: that mighty event which shook and continues to shake the pillars of the global crusade," on Tuesday, to mark the anniversary of the September 11th attacks.
Zawahiri, an Egyptian who took up the reins of Al-Qaeda after the killing of Osama Bin Laden in June, hailed popular uprisings that have toppled leaders in Egypt, Tunisia and Libya this year, and urged other Muslims to overthrow their own rulers.
"The Arab people have been freed from the chains of fear and terror, so who is the winner and who is the loser?"
Many analysts say Al-Qaeda lost relevance as a result of the political upheaval across the Middle East and North Africa, where hundreds of thousands of people called for democratic reform and the militant group often played little or no role.
In the hour-long recording, titled "The Dawn of Imminent Victory," Zawahiri expressed hope the fall of Arab rulers he said were in thrall to the West would usher in an era of true Islam and sharia-based governance.
"The blessed rebellious Arab earthquake has turned America's calculations head over heels," he said. He said the United States had lost key regional allies in the upheaval.
The video also included a message from Bin Laden, which Zawahiri said was being aired for the first time. The exact date of the clip was not clear.
In it, Bin Laden warned Americans of the "tyranny" of capitalism and big corporations, which he said were a main cause of war and had brought the United States to the brink of bankruptcy. He did not mention the "Arab Spring."