New al Qaeda leader Ayman al-Zawahri voiced support in an Internet video for popular revolts shaking the Middle East, saying Arabs no longer feared the United States 10 years after the country was targeted by the militant network.

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, Zawahri said in the video posted on Islamist websites on Tuesday to mark the anniversary of the September 11, 2001 attacks.

Zawahri, an Egyptian who took up the reins of al Qaeda after the killing of Osama bin Laden in May, hailed popular uprisings that have toppled leaders in Egypt, Tunisia and Libya this year, and urged other Muslims to overthrow their rulers too.

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 has lost relevance as a result of the political upheaval across the Middle East and North Africa, where hundreds of thousands of people have called for democratic reform and the militant organisation has played little or no role.

In the hour-long recording, titled The Dawn of Imminent Victory, Zawahri expressed hope that 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, adding the United States had lost key regional allies in the upheaval.

We ask God that the spring of strength and liberation be the bitter winter of America and a dark tunnel from which it will not emerge except in defeat, Zawahri said in the audio message played over a still photograph of him brandishing a gun.

Zawahri called on Syrians to persevere in their struggle against the corrupt and criminal rule of President Bashar al-Assad and welcomed the overthrow of Libyan leader Muammar Gaddafi, though he criticised NATO's involvement.

The video also included a message from bin Laden, which Zawahri 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 primary cause of war and had brought the United States to the brink of bankruptcy.

He did not mention the Arab Spring of popular uprisings.

Zawahri asked Muslims worldwide to focus their efforts on fighting the United States.

I encourage every Muslim who desires his nation's freedom to undertake to hurt America for the more we put pressure on it, the freer we will be from its agents.