BEIRUT (AP) — Heavy fighting broke out Monday between rival jihadi groups in an oil-rich eastern Syrian province bordering Iraq, forcing many residents to flee, activists said.

The Britain-based Syrian Observatory for Human Rights said the fighting concentrated on the eastern parts of Deir el-Zour province. An activist based in the province who goes by the name of Abdul-Aziz Sheik said many tribesmen have joined the battle on the side of the Syrian al-Qaida affiliate known as the Nusra Front, which is fighting an al-Qaida breakaway group, the Islamic State of Iraq and the Levant.