ISIS has vowed to step up attacks on US-backed Kurdish forces in eastern Syria, the group has announced in a video posted to its media channels. The Kurdish-led Syrian Democratic Forces recaptured the last territory in Syria held by the militant extremist group in late March, ending the yearslong military campaign to defeat their so-called “caliphate”. The village of Baghouz in Deir Ezzor province was the last to fall with support from coalition air strikes. "The fire of the battle between us and them has been reignited and will intensify," the militant group said on Sunday in a message on the encrypted messenger Telegram. The message was addressed to what it called "soldiers of Islam" and residents of the caliphate. ISIS took swathes of oil-rich land in Iraq and Syria in a lightning 2014 offensive. Since the loss of its proto-state, IS has retained sleeper cells and has orchestrated a series of car bomb and arson attacks in eastern and northeastern Syria since its territorial defeat. They have also been carrying out ambushes and hit-and-run attacks in Iraq. In Sunday's video – the second since the fall of Baghouz – ISIS accused coalition countries of having entrapped its local adversaries, including the Kurds. "They have been thrown into the flames of a fierce war that will leave them without tail or head," ISIS warned. The video includes decapitations and the shooting to death at close range of people presented as kidnapped Kurdish fighters. ISIS released a video in late April – shortly after claiming deadly attacks in Sri Lanka – in which a man appearing to be leader Abu Bakr Al Baghdadi was seen pledging vengeance and a "long battle" ahead. A US Defence Department report said this month that ISIS was "resurging" in Syria, while it had "solidified its insurgent capabilities in Iraq". The Defence Department also named a US marine killed in Iraq over the weekend as 35-year old Gunnery Sgt Scott A. Koppenhafer. The US soldier was killed after being hit by enemy small arms fire while accompanying and advising Iraqi security forces in Ninevah province. He was deployed as part of Operation Inherent Resolve, the US-led mission to defeat ISIS. Koppenhafer enlisted in 2005 and had been with Special Operations Command for 10 years having served previously in Afghanistan. He had earned two Bronze Stars.