An offensive began on Monday against an estimated 2,000 fighters
ISIS holdouts under siege in Syria by regime and US-backed forces
The last remaining pockets of ISIS territory in Syria, including villages where the group's leader Abu Bakr Al Baghdadi is rumoured to be hiding, are under attack and surrounded by government and US-backed forces.
While the extremists are reverting to an underground insurgency that is likely to pose a threat for years to come, the capture of its last pieces of territory would be a symbolic defeat.
However, on Wednesday the US warned that an impending assault in the northwestern province of Idlib could harm operations.
At its peak, ISIS controlled major cities across Iraq and Syria, ruling over an estimated 10 million people. That territory has been steadily reduced since 2014.
Today, it has a presence in three pockets of mostly barren territory in Syria – the As-Safa volcanic field in the south, a patch of desert to the east of Palmyra, and several towns on the eastern banks of the Euphrates River near the borders of Iraq and Jordan.
The first two areas are under attack from the Syrian army, while the territory on the Euphrates is the target of an offensive by Arab and Kurdish fighters of the US-backed Syrian Democratic Forces (SDF).
The SDF offensive began on Monday and aims to "clear remnants of (ISIS) from northeastern Syria along the Middle Euphrates River Valley toward the Syria-Iraq border," the US-led coalition to defeat ISIS said.
Around 60,000 civilians are thought to live in the town of Hajin and villages along the river, which together represent the last populated area still under ISIS control. It is also the area to which many believe the top leaders of ISIS are hiding out.
Iraqi and US intelligence officials have spoken in the past of having information placing Baghdadi around Hajin. US Secretary of Defence James Mattis told reporters on Tuesday that he "wouldn’t be surprised" if ISIS leaders were still in the area, while declining to give more details.
He said he "wouldn’t be surprised" if ISIS leaders were in the area, while declining to give more details.
The coalition estimates that as many as 2,000 ISIS fighters could be bunkered down. The operation is being backed by artillery and air support from coalition forces, who predict a tough fight.
"The battle will be difficult, and possibly lengthy, as we believe a lot of foreign fighters that have nowhere to go will fight to the end. This includes the ideology strong fighters that would rather detonate a suicide vest than be captured," Colonel Sean Ryan, a spokesman for the coalition, told The National.
"We know ISIS has built defensive positions, has an underground tunnel system, still has a weapon capabilities like artillery, but believe IEDs will be one of their main focuses," he said.
A video released by the ISIS-run Amaq News Agency on Tuesday gave an indication of how fierce the battle could be. The group claimed to have repelled an attack near the village of Al-Bagouz, and filmed the bodies of five SDF fighters it said were killed in the battle.
Syria Civil War
Bombings in Syria's Idlib drive more than 30,000 from their homes
The UK-based Syrian Observatory for Human Rights said 27 ISIS members and 10 SDF fighters have been killed since Monday near Hajin.
Elsewhere in Syria, ISIS is facing dual Syrian army attacks in two barren hideouts in the south and east of the country.
To the east of the city of Sweida, the Syrian army has surrounded the As-Safa volcanic field – a striking plateau of rolling black hills visible from space.
ISIS fighters have used the rocky terrain as a hideout for years as they carried out attacks in the south. The group reportedly killed 12 Syrian soldiers in an ambush in the area late on Monday, but the Syrian army has been making steady progress.
The Syrian army launched an offensive to recapture the large stretch of desert where the field lies after an attack on the Druze city of Sweida by ISIS fighters in July that left more than 200 dead. ISIS also kidnapped dozens of women and children in the attack, most of whom are still held by the group.
Meanwhile, in the desert to the east of Palmyra, the Syrian army reportedly cleared hundreds of square miles of previously ISIS-held territory on Tuesday.
Unlike in previous offensives, the ISIS fighters have not been left an escape route and may fight to the death.