BEIRUT — Fighting in eastern Syria between Islamic rebel brigades and an Al-Qaeda splinter group has killed more than 630 people and uprooted at least 130,000 since the end of April, an activist group said Tuesday. The clashes in Deir El-Zour province, which borders Iraq, are part of broader rebel-on-rebel clashes that have raged across opposition-held northern Syria since early January. The violence pits rebel groups, including the Al-Qaeda-affiliated Nusra Front, against the Islamic State of Iraq and the Levant, which was disavowed by the terrorist network earlier this year because of its brutality. This war-within-a-war has been a massive drain on resources and manpower on the opposition in Syria, undermining its fight against President Bashar Al-Assad in the wider civil war. The Britain-based Syrian Observatory for Human Rights said the fighting in Deir El-Zour alone has killed 634 since April 30. It said the tally includes 39 civilians, 354 rebel fighters, including many from the Nusra Front, and 241 gunmen from the Islamic State. Once spread across much of northern Syria, the Islamic State withdrew many of its far-flung fighters to its stronghold in the northern city of Raqqa earlier this year after other rebel factions, furious with the Islamic States' efforts to impose its hard-line interpretation of Islam, launched an offensive against the group. But the Islamic State has since consolidated its hold on Raqqa and the surrounding province. Then in early May, its fighters pushed onward to the neighboring province of Deir El-Zour, capturing villages and towns along the Euphrates River and closing in on the provincial capital, the city of Deir El-Zour. The group was once welcomed by some Syrian rebels, but earned the rebellion's wrath because of its systematic abuses and quest for hegemony. Even Al-Nusra turned against ISIL, after its Iraqi chief, Abu Bakr Al-Baghdadi, sought to take over the group. Syria's war has killed more than 162,000 people and forced nearly half the population to flee their homes. — Agencies