The six largest Islamist rebel factions in Syria declared a new Islamic Front on Thursday, forming the largest alliance of opposition fighters yet in the 2-1/2-year conflict. "This independent political, military and social formation aims to topple the Assad regime completely and build an Islamic state where the sovereignty of God almighty alone will be our reference and ruler," said Ahmed Eissa, who heads the Suqour al-Sham brigades. It could also challenge the ascendance of al Qaeda-linked factions who have grown increasingly powerful as other rebel groups are weakened.