Al-Qaida leader Ayman al-Zawahiri has called on militant groups in Syria to unite and "defend jihad", until the country is "free of the Christian, secular regime and its aids".

"My Muslim brothers and mujahideen in Syria and everywhere, our duty today is to defend jihad in Syria against conspiracies being woven by the followers of the UK and the US; the House of Saud and their supporters in the region," Ayman al-Zawahiri said.