A group of Islamist Syrian rebels who oppose Islamic State have released a video of their slaughter of 13 terrorists in a graphic parody of the murder tactics of their enemies.
Wearing orange boiler suits similar to those usually worn by the victims of Islamic State, the Jaysh Al-Islam soldiers have reportedly killed dozens of Islamic State fighters.
The rebel group represents a merger of more than factions that oppose Al-Qaeda and Islamic State. It is believed to have about 25,000 soldiers.
Jaysh al-Islam released the video shortly after Islamic State published one of their own, in which they behead 12 Jaysh al-Islam militants near Damascus.
As they await their execution, the video shows the Jaysh Al-Islam or Army of Islam commander addressing the Islamic State terrorists, saying: "Allah did not make a disease without appointing a remedy to it."
The Islamic State terrorists are given a drink, their faces are shown and then they are shot in the head.
Before they are shot, a Jaysh Al-Islam soldier says: "The most serious calamity for our jihad today is a group of people who grow at a time of division among Muslims.
"This group claimed to be the mother state and made Takfir, ie accused of apostasy, on other Muslims, shed their blood and looted their properties and dignities.
"They worsened the ordeal of Muslims by corrupting their religion and livelihood and killing the jihadi leaders who did their best to help our stricken nation.
"They wreaked havoc on our people in liberated areas and cut the supply route of jihadis.
"They left Tehran intact and instead they attacked our mosques.
"This is the penalty for what they have committed.
"We also call on their fellows to repent."
Charlie Winter, an analyst with the counter-extremism think-tank Quilliam, told the Independent that the killings and recording were probably carried out a while ago. Trailers of the video were first released a week ago.
He said: "Even though the killing was done way back, there was doubt as to whether the video would be released. Isis goaded Jaysh al-Islam into it. And, seeing Isis's reaction on Twitter, it is so clear that this was the desired effect."
