The Islamic State in Iraq and the Levant group has publicly executed a Syrian it accused of planting tracking devices for deadly government air strikes, according to the SITE intelligence group.
SITE posted footage of the accused being paraded before a crowd but the video deliberately freezes at the point an ISIL fighter pulls his head back and holds a knife to his neck.
After the execution, in Syria's northern Aleppo province, the fighters paraded the body of the accused on a cross.
ISIL claimed that that more than 190 people had been killed in the air strikes that the man had abetted.
In October and November, the Syrian government sharply intensified its air strikes on areas held by ISIL or other rebel groups.
In just 40 days, about 2,000 strikes killed more than 500 people, the Britain-based Syrian Observatory for Human Rights said.
Some of the deadliest hit the ISIL "capital" of Raqqa on November 25, killing at least 95 people, but air strikes have also hit the group in the eastern part of Aleppo which they control.
ISIL has earned drawn the world's attention with its release of video footage of its executions of Western hostages, captured soldiers and civilians accused of breaching its version of Islamic law.
In the latest instance, a French-speaking fighter threatened on Friday to execute Lebanese soldiers held hostage by ISIL, saying three prominent anti-ISIL Lebanese politicians would be responsible for their deaths.
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The threat was made in a video AFP news agency obtained from Wissam al-Masri, a Salafist religious leader who is mediating the release of 25 police and soldiers held by ISIL and the Syrian branch of al-Qaeda, al-Nusra Front.
Four hostages have already been executed.
The video, filmed in a field with hills in the background, shows three men in blue uniforms, each kneeling in front of a fighter holding a knife to his throat.
The unidentified speaker was wearing a hood and his companions' faces were uncovered. From his speech, it was not possible to determine if he was from Lebanon, where French is widely spoken, or a third country.
Thousands of fighters from France and countries in North Africa where French is spoken have flocked to ISIL ranks.
The speaker attacked the politicians for what he said is their support for Lebanon's mainly Shia group Hezbollah, whose fighters are aiding Syrian President Bashar Assad in the civil war against largely Sunni Muslim rebels that include ISIL.
"To the allies of France in Lebanon - Hariri, Geagea and Jumblatt - the Islamic State is at war with Hezbollah, which is meddling in the affairs of Muslims in Shams [Syria] and has killed our women and our children," he said, referring to Saad Hariri, a Sunni former prime minister; Samir Geagea, a Christian leader; and Walid Jumblatt, chief of the Druze community in Lebanon.
In a separate development, al-Qaeda fighters seized dozens of tanks and armoured personnel carriers from the Syrian army when they took two government bases this week, the Syrian Observatory said on Friday.
Al-Nusra Front captured the Wadi al-Deif and Hamidiyeh military posts in the northwestern province of Idlib on Monday, the Syrian Observatory said.
The monitoring group, which relies on a network of sources on the ground, had said in an earlier report that nearly 200 combatants on both sides were killed in a 24-hour battle for the bases.
Al-Nusra Front fighters, backed by allied rebels, captured at least 120 soldiers, the Observatory said at the time.
On Friday the Syrian Observatory reported that al-Nusra Front also seized 35 tanks and 20 armoured personnel carriers "stuffed with ammunition".