Al Qaeda's second-in-command Ayman al-Zawahri
Al Qaeda's Ayman al-Zawahri appears in a 2011 video Reuters

Al-Qaeda's leader has called on his followers to switch tactics and engage in guerrilla warfare as they prepare for protracted jihad [holy war] in Syria.

In an audio statement released by the terrorist group's propaganda arm, As Sahab, Ayman al-Zawahri called for his Syrian Sunni jihadists to prepare for a "long battle" against Syrian President Bashar al-Assad and well as the US-led coalition.

Zawahri, the successor to Osama Bin Laden, said an "international satanic alliance" will never accept Islamic rule in Syria and that Muslims across the world, not just those in Syria, should fight for divine rule.

He said the West and its allies have been targeting them in order to prevent an "Islamic" wave that is sweeping the region.

Zawahri said: "In my humble opinion the strategy for jihad in Sham must focus on a guerrilla war aimed at wearing down the enemy and bleeding it to death," reported the Long War Journal.

Al Qaed's Syria branch Fatah al-Sham Front, formally known as Nusra Front, is currently spearheading the attacks on the Syrian government as well as their Russia and Iran-backed allies in Syria.

Iraqi Vice President Ayad Allawi previously warned that al-Qaeda are attempting to form an alliance with Isis in order to help battle forces in Mosul.

He said: "The discussion has started now. There are discussions and dialogue between messengers representing [Isis leader Abu Bakr al ] Baghdadi and representing Zawahiri."