Nearly half the rebel fighters in Syria are now aligned to jihadist or hardline Islamist groups according to a new analysis of factions in the country's civil war.
Two factions linked to al-Qaeda, Jabhat al-Nusra and the Islamic State in Iraq and the Levant (ISIL) - also know as the Islamic State of Iraq and al-Shams (ISIS) - have come to dominate among the more extremist fighters.