In a wide ranging audio interview, the al-Qaeda leader expressed solidarity with the Muslim Brotherhood which is facing a violent crackdown by the army-backed government in Egypt and urged unity among terrorists in their fight against the Syrian government.

"I ask Allah the Glorious to help us set free Dr. Omar Abdel-Rahman and the rest of the captive Muslims, and I ask Allah to help us capture from among the Americans and the Westerners to enable us to exchange them for our captives," said Zawahiri, according to the SITE website monitoring service.

Abdel-Rahman is serving a life term in the United States for a 1993 attack on New York's World Trade Center.

Zawahiri also urged war against Syria and renewed his call to end infighting among terrorist groups that increased this year, pitting the Islamic State of Iraq and the Levant (ISIL) against rival militants including other hardline extremists.

"The Ummah (Muslim world) must support this jihad with all that it can, and the mujahideen (extremist militants) must unite around the word of Tawhid (monotheism)," claimed Zawahiri, an Egyptian-born doctor.

"So everyone should prioritize the interest of Islam and the Ummah over his organizational or partisan interests, even if he gives up for his brothers what he sees as right."

Al-Qaeda said it was breaking with ISIL in February after disputes over the group's refusal to limit itself to fighting in Iraq rather than in Syria, where the Nusra Front is al-Qaeda's affiliate.

Asked about the crackdown on the Muslim Brotherhood in Egypt, Zawahiri answered: "the duty of every Muslim is to deter the aggressor by any means."

Egyptian security forces have suppressed Brotherhood supporters and arrested thousands, including most of its leaders, since the army toppled Islamist President Mohamed Morsi on July 3 following mass protests against his rule.

NTJ/HH