Al Qaida's leader has urged his followers and all militants in Syria to unite ranks and prepare for protracted jihad.
Ayman al-Zawahri told the jihadis to remain steadfast and change tactics to guerrilla warfare.
His remarks came in an audio message released on Monday by al Qaida's media arm, As-Sahab.
Al-Zawahri said an "international satanic alliance" will never accept Islam's rule in Syria.
He said the war is not an exclusively nationalist Syrian cause, but a campaign by the entire "Muslim nation" which seeks to establish divine rule.
Al Qaida's Syrian branch - formerly the Nusra Front, but now known as the Fatah al-Sham Front - has come under increasing attack from the US-led coalition in recent months and some of its most senior leaders have been killed in air strikes.