In an audio message credited to Al Qaeda's top leader, the speaker praises last month's deadly attack on a U.S. Consulate in Libya and calls for more protests against offensive depictions of the Prophet Mohammed.
"May God salute the free honest believers who stood up and stormed the American Consulate in Benghazi and those who demonstrated in front of the American Embassy in Cairo and brought down the American flag and raised the banner of Islam and Jihad instead," Ayman al-Zawahiri says in the purported audio message posted on various Islamist websites overnight.
CNN could not confirm the authenticity of the audio.
While the speaker mentions the Benghazi attack, he says nothing of its outcome: Four Americans, including Ambassador Chris Stevens, were killed.
It's not clear when the seven-minute message was recorded.
The attack on the U.S. Consulate coincided with protests around the Muslim world against an anti-Islam movie produced in the United States, called "Innocence of Muslims."
U.S. officials have said the attack in Benghazi was planned, but took advantage of the demonstrations that raged against the movie.
"In the pretext of personal freedom and freedom of expression, America allowed the production of a movie that was aimed to defame the beloved Prophet Mohammed, even though this alleged personal freedom that they boast about didn't stop the Americans from torturing the Muslim prisoners" at U.S. facilities, the audio recording says.
"I call upon (protesters) to continue their confrontation against the American Zionist crusader transgression and I call upon all Muslims to follow their leads," he says.
Al-Zawahiri was last heard in a video released in September, where he showed an interest in exploiting violence in Syria.