Fighters from an Al-Qaeda-linked group expelled rival rebels from a northern Syrian town after heavy clashes Monday, then quickly moved to eliminate any pockets of resistance by setting up checkpoints on major roads and conducting house-to-house raids in search of opponents, activists said.

The Islamic State of Iraq and the Levant's seizure of the town of al-Bab is part of a brutal battle between the Al-Qaeda-affiliated group and rebels from Islamist and more moderate factions that has raged across opposition-held territory in northern Syria for the past 11 days. The rebel-on-rebel clashes are the most serious since the Syrian civil war began, and have further muddied an already complicated conflict less than two weeks ahead of a planned international peace conference for Syria in Switzerland.

The pace and scale of the rebel war-within-a-war has eclipsed even that of the opposition's fight against President Bashar Assad, with at least 700 people killed since the infighting began Jan. 3, according to the Britain-based Syrian Observatory for Human Rights.

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