Baghdad, Iraq: The Islamic State group strung up four Iraqi Shiite fighters with chains and burned them alive, according to footage posted online, the latest gruesome execution video from the jihadists.

The victims—identified as fighters in the pro-government Popular Mobilisation forces from southern Iraq—were suspended from a swingset by chains attached to their hands and feet, then set on fire.

IS, which overran large parts of Iraq last year and still controls much of the country’s west, said the murders were in revenge for the alleged burning of four men by pro-government forces.

‘Now retribution has come, for today, we will attack them as they attacked us, and punish them as they punished us,’ a masked militant says in the video, which was not dated and did not say where the burnings took place.

The video included a clip said to show a Sunni man suspended over a fire while still alive as pro-government forces look on, and another of famous Shiite fighter Abu Azrael (‘Father of the Angel of Death’) slicing a piece of flesh off a burned corpse with a sword.

IS has carried out a slew of atrocities in territory it controls in Iraq and Syria, such as mass executions and a campaign of killings, kidnapping and rape targeting minorities.

It has recorded many killings—including beheadings, shootings, drownings and burnings—in videos posted online.