The video shows militants shooting three men execution-style outside of the city of al-Raqqa.
Militants are later seen throwing the dead bodies into a cleft in the rocks a few kilometers south of the execution site.
Earlier in the month, heavy clashes broke out between ISIL militants and the al-Qaeda-linked al-Nusra Front and Ahrar al-Sham in the eastern city of Deir Ezzor.
The ISIL militants also clashed with Kurdish fighters in the northeastern province of Hasakah.
Months of infighting between various armed groups have left thousands of Takfiri militants dead in Syria.
Syria has been gripped by deadly violence since March 2011. Over 160,000 people have reportedly been killed and millions have been displaced due to the violence fueled by the Western-backed militants.
The West and its regional allies including Qatar, Saudi Arabia, and Turkey are giving financial and military support to the militants.
The foreign-backed militancy in Syria has spilled over into neighboring Iraq.
Some political commentators believe the crisis in Syria will backfire on the West as militants are now returning to the countries they came from, including those in Europe.