Al Qaeda chief Ayman al-Zawahiri urged Muslims to keep up their protests against an anti-Islam film produced in the US, in a speech published on jihadist forums on Saturday.

In the seven-minute audio, Zawahiri hailed "the honourable people... who stormed the US embassy in Benghazi and those who protested outside the US mission in Cairo where they replaced the US flag with that of Islam and jihad".

The amateurish film depicting the Prophet Muhammad as a thuggish deviant offended many Muslims and sparked anti-US protests in a number of countries that cost several lives and saw mobs set US missions, schools and businesses ablaze.

Zawahiri called on those who protested "to continue to counter the US-Crusader-Zionist attack on Islam and Muslims and urge other Muslims to follow suit".

He condemned the US "whose laws allow attacks on the Muslim prophet and their holy book (the Quran), in the name of freedom of expression, while charging those who attack Jews with anti-Semitism".

Other affiliated groups such as al Qaeda in the Arabian Peninsula and al Qaeda in the Islamic Maghreb have made similar statements on the film Innocence of Muslims.