The Britain-based Syrian Observatory for Human Rights says battles are still raging today, for a second day, around Bukamal town in the oil-rich Deir el-Zour province near the Iraqi border.
Rebels from the al-Qaeda breakaway group known as the Islamic State of Iraq and the Levant and fighters of the al-Qaida-linked Nusra Front and other Islamic groups have been fighting each other in the province for weeks over territory they previously captured together from President Bashar Assad's forces, including oil-fields.
The Observatory said 51 fighters died in fighting around Bukamal yesterday, when the flare-up started. The Islamic State captured the town, previously controlled by the Nusra Front.