Six men accused of leaking sensitive information about the Islamic State group to the Iraqi government were executed on video, the Daily Mail in the U.K. reported Thursday. The grisly killings reportedly were carried out in the extremist group’s besieged stronghold of Fallujah in Anbar province, where the Iraqi military has recently been making gains against the militant group.

A hospital worker was decapitated by a blue explosive wire wrapped around his neck after he was accused of relaying information about ISIS medical staff. Two policemen were shot, execution-style, in a separate clip, after they were charged with attempting to leave Fallujah to pass on information to the Iraqi military. Two other men accused of so-called apostate crimes were killed the same way. And a sixth man, a policeman accused of handing over information, was beheaded.

isis Militant fighters participate in a military parade in the northern Raqqa province of Syria June 30, 2014. Photo: Reuters/Stringer

The gruesome video has surfaced as the Iraqi military, backed by U.S.-led coalition airstrikes, has pushed forward an offensive targeting ISIS in Anbar province. Captured by the extremist group in 2014, Fallujah is currently surrounded by the Iraqi military and has been cut off from the rest of the militant group’s so-called caliphate. The situation in the city is growing desperate, Reuters reported this month, as tens of thousands of trapped civilians are running out of food and medicine. It’s unclear when the video was made, but its production appears to match other videos released by ISIS and subsequently confirmed by experts.

The video was seen by some as an attempt to show ISIS still controlled Fallujah. Text shown in the video said it should serve as “a message to the apostates and their masters that blood for blood and destruction for destruction.”

A longtime militant hub, Fallujah was the first Iraqi city to fall to ISIS two years ago. After its military success there, the extremist group made a number of other gains in the war-torn country, including the takeover of its second-largest city, Mosul. More recently, however, the militant group’s grip has steadily been loosening. During the past 15 months, ISIS has lost almost one-quarter of its territory, according to data reported by IHS Wednesday.

This week, U.S. State Department representative John Kirby said there had been a growing number of defections in ISIS’ ranks recently, as fighters have become increasingly disillusioned with the extremist group. As a result, the militant group has pushed children to the front lines in an attempt to bolster its shrinking forces. Meanwhile, the U.S.-led campaign has kept up the pressure by targeting ISIS’ revenue sources, reportedly leading the group to cut fighters’ salaries and impose new taxes.