Ousting the last Islamic State group fighters from Raqa will be tough, but the jihadists are breathing their "last gasps" in their Syrian bastion, a senior US-led coalition commander told AFP.

Those defending the city would not be allowed to withdraw, and the coalition has already set its sights on a prized IS-held city further east, the commander said at a coalition compound near Kobane, in northern Syria.

After a months-long campaign, the Syrian Democratic Forces -- a US-backed alliance of Arab and Kurdish fighters -- have cornered diehard jihadists in a pocket of territory in the battered northern city of Raqa.

"It's a tough fight. There's a lot of (IS) foreign fighters there that don't want to give up and intend to fight very hard," the top coalition commander assisting and advising the SDF said, speaking on condition of anonymity.

"They're isolated in this small section that's left, but they're not isolated alone," with civilians and family members trapped inside along with jihadists.

Now surrounded, IS fighters would likely lash out in "last gasps," but a negotiated withdrawal would be unacceptable, the commander said.

"The enemy inside Raqa needs to surrender or be destroyed in Raqa because if they sneak out, they'll find a way to get to Europe or neighbouring countries, or attack places outside of Syria," he added.

- New hub targeted -

Since IS captured it in 2014, Raqa served as the de facto Syrian capital of the group's self-styled Islamic "caliphate" and was long thought to be the main hub for planning attacks abroad.

But now, the coalition believes that headquarters lies in a strategic eastern city that will form their next target.

"We're going for Al-Mayadeen. There are a lot of folks in Al-Mayadeen who plot external attacks on our homelands, on coalition homelands, so we can't allow it to remain an IS sanctuary," the commander said.

The city lies in Syria's oil-rich Deir Ezzor province, where the US-backed SDF and Russian-backed government forces are waging rival offensives against IS territory on either side of the Euphrates River.

A "de-confliction" line is supposed to prevent the two campaigns from clashing, but the SDF has twice accused Russia and the regime of bombing its fighters in the province.

Asked how a race between the SDF and regime forces over Al-Mayadeen could play out, the commander said it "has the potential to be chaotic but isn't chaotic (yet)."

"If Al-Mayadeen is like Deir Ezzor, with the two forces on either side, then we will have to de-conflict very closely. If one of us is there first, then it will be pretty straightforward."

The coalition is backing both SDF operations on Raqa and Deir Ezzor with air strikes, special operations advisers, weapons, and other equipment.

"The coalition help means the SDF faces fewer casualties, moves a little faster, and is less subject to enemy attack," the commander said.

- 'Sealed the deal' -

As fighting in Raqa moved into highly populated quarters, coalition and SDF forces began opting for "precise" weapons like mortars and artillery instead of air strikes, he said.

But the decisive factor in the SDF's progress was its inclusion of Arab fighters alongside experienced Kurdish militiamen, according to the commander.

"When they decided to do Raqa with a very large Arab component, they sealed the deal in making it work the right way," he said.

The coalition says it has trained 9,000 SDF members, most of them Arabs including Raqa natives.

Much of Raqa has been reduced to ruins by nearly four months of fierce fighting inside the city itself, in addition to several years of air strikes against IS targets.

"There's no question that the citizens of Raqa have a lot of work ahead of them," the commander said, but added he "didn't know how else" the operation could have succeeded against IS.

"You just have to do your best to keep the destruction as minimal as possible without letting the SDF just get killed."

Source: AFP