BEIRUT (AP) -- Tribesmen have risen up against the extremist Islamic State group in eastern Syria, forcing it to withdraw from three villages after heavy clashes that killed more than a dozen people, activists said Saturday.
The violence in eastern Syria came amid tension on the border with Lebanon after an ambush killed dozens of opposition fighters, activists say. The Lebanese army said in a statement that troops also detained Syrian citizen Imad Ahmad Jomaa, who identified himself as a member of Syria's al-Qaida-linked Nusra Front.
A Lebanese army general told The Associated Press that after Jomaa's capture, gunmen deployed in Lebanon's border village of Arsal near army positions. He said the government sent reinforcements to the area. He spoke on condition of anonymity as he wasn't authorized to speak publicly.
Arsal is home to tens of thousands of Syrian refugees and rebels enjoy wide support among its population. Syria's civil war has spilled over to Lebanon on several occasions, leaving scores dead.
The tribesmen's rise against the Islamic State group was the first sign of local resistance to the extremists since its fighters captured large parts of the oil-rich eastern province of Deir el-Zour in recent weeks.
The Syrian Observatory for Human Rights and Turkey-based activist Mustafa Osso said the group was forced to bring in reinforcements from neighboring Iraq after members of the Shueitat tribe drove jihadi fighters out of the villages of Kishkiyeh, Abu Hamam and Granij.
The Observatory, a Britain-based group relying on activists inside Syria, said tribesmen torched the local headquarters of the Islamic State group in the nearby town of Ashara and that residents demonstrated against the group.
Osso and the Observatory said fighting first broke out Wednesday after jihadis detained three tribesmen, allegedly breaking an agreement between the two sides reached after Islamic State fighters captured the villages.
The al-Qaida breakaway Islamic State group took over large swaths of western and northern Iraq in June. The group has declared a self-styled caliphate in territory it controls along the Iraqi-Syrian border, imposing a harsh interpretation of Islamic law.
"There has been wide resentment recently because of Islamic State's acts," said Osso, who is in contact with activists in different parts of Syria. He said one of the group's top commanders, an ethnic Chechen known as Omar al-Shishani, is believed to be leading the jihadis in the area.
Osso added about Deir el-Zour: "This is a very important area for Islamic State because it is rich with oil and borders Iraq."
The Observatory said tribesmen captured the nearby Tanak oil field Friday. It added that the Islamic State group has sent a large number of fighters from the Iraqi border town of Qaim to reinforce the group's positions.
The Observatory said four days of fighting killed nine jihadis, three tribesmen and five civilians.
In a separate incident, the Observatory said Syrian troops and members of Lebanon's Hezbollah group ambushed a large number of opposition fighters in the Qalamoun region near the Lebanese border Saturday, killing at least 50 of them. It said seven troops and Hezbollah fighters were killed in the fighting.
Syrian state television reported clashes in Qalamoun that killed "tens of terrorists." Syrian media refers to all opposition fighters as terrorists.
Government troops backed by Hezbollah fighters have seized nearly all the strategic Qalamoun region since launching an offensive there last November, severing rebel supply lines from neighboring Lebanon.
The Syrian uprising began in the form of peaceful protests against President Bashar Assad in March 2011, but escalated into an insurgency when government forces violently cracked down on dissent.
The country is now in the grip of a complex civil war pitting several rebel and Islamic extremist groups against the government and each other. Over 170,000 people have been killed in Syria in more than three years of fighting, activists say.