OPPOSITION fighters have battled rival al Qaida-linked rebels in northern Syria as deep fissures within the uprising erupted into some of the most serious violence between groups opposed to President Bashar Assad since the conflict began.

The clashes, which have spread to parts of four provinces, pit an array of moderate and ultra-conservative Islamist brigades against the Islamic State of Iraq and the Levant, an extremist group that has become both feared and resented for trying to impose its hard-line interpretation of Islam.

The fighting did not appear to be a turn in unison by Syrian rebel groups against the Islamic State of Iraq and the Levant but rather an outburst of violence against the al Qaida-linked group in communities where tensions with other opposition factions were already simmering.

In some parts of northern Syria, the backlash has been brewing for months.