Activists say tribesmen have risen up against the extremist Islamic State group in eastern Syria, forcing it to withdraw from some villages.

The Britain-based Syrian Observatory for Human Rights and Turkey-based activist Mustafa Osso on Saturday said the group was forced to bring in reinforcements from neighboring Iraq.

They said members of the Shueitat tribe in Syria's oil-rich eastern province of Deir el-Zour forced jihadi fighters to withdraw from the villages of Kishkiyeh, Abu Hamam and Granij.

They said fighting first broke out Wednesday after jihadis detained three tribesmen.

The al-Qaida breakaway Islamic State took over large swaths of western and northern Iraq in June. The group has declared a self-styled caliphate in territory it controls in Iraq and Syria, imposing a harsh interpretation of Islamic law.