DW: The Syrian city of Raqqa is now the de facto capital of the so-called "Islamic State" (IS). What is its significance for the terrorist militia?

Guido Steinberg: Raqqa is the second-most important city in IS-held territory. Mosul in Iraq is much more significant. That's where IS had its Iraqi organization, that's where it declared its caliphate, and that's where it has survived difficult times in the past. But Raqqa is also important because it's the Syrian capital of IS, and has served as a sort of retreat. It has been easier for IS to operate in Syria than it has been in Iraq, because its opponents are stronger there.

But isn't Raqqa also considered to be the financial center of IS? It has also served as an external operations base to plan attacks in the West - the attacks in Paris, for example.

It's true that the foreigners in the organization are much more strongly represented in Syria. The division for foreign operations, which was until recently headed by Abu Mohammed al-Adnani, operates out of Raqqa. [Editor's note: al-Adnani was killed in an attack in August 2016] Most of the group's foreign fighters and their leaders are stationed in Raqqa. When it comes to planning attacks in Europe and Turkey, Raqqa is much more important than Mosul. You could describe Raqqa as a kind of upstream operational base.

The Syria Democratic Forces (SDF) are leading the offensive with the support of the United States. It is a coalition of 30,000 fighters, mostly of Kurdish origin, although it also includes Arab fighters. What problems do these fighters face in the "Wrath of the Euphrates" operation that's now underway?

The SDF is a euphemism, covering up the fact that we're talking almost exclusively about Kurdish forces, and specifically, Kurdish members of the Democratic Union Party (PYD), a Syrian branch of the PKK, or Kurdistan Worker's Party. And for foreign policy reasons, that poses difficulties especially for relations with Turkey. It's also problematic for the Raqqa operation. Raqqa is an Arab city, and its Sunni-Arab residents would see Kurdish rule - or even just a Kurdish victory - as an occupation. It's possible that the residents would support IS or any remaining terror cells if the Kurds are the ones leading the charge here. There may be a couple thousand Arabs taking part, and the US has made a tremendous effort over the last two years to bring more Arab fighters on board. But this remains a force that is dominated by the PKK or PYD. And even if that weren't the case, it matters a lot how the population perceives the situation. And they perceive this force to be a Kurdish unit.

If the SDF does manage to liberate Raqqa, who would have control over the city in the future? The Kurds, who want to expand their territory in northern Syria?

If the SDF does manage to take Raqqa, it would be an utmost necessity to hand control over the city to Arab militias. But up to now I've had the impression that they are much too weak to take on the management of such a big city. This problem needs to be resolved. My feeling is that there is now a sense of urgency to liberate Raqqa because the US has information that concrete attacks on the Western world are currently being planned there.

What would the liberation of Raqqa mean in terms of the dynamic in the Syrian conflict? Or is Aleppo the more important city?

We are now dealing with two different levels of conflict in Syria. We have the fight against IS, which is almost completely separate from the civil war between the rebels and the Syrian government. The liberation of Raqqa would initially help to alleviate the immediate problem of IS. It wouldn't mean that the group has been defeated, but it would certainly impede the planning and organization of terrorist attacks. The liberation of Raqqa would barely have any effect on the battles being fought in the western part of the country around Aleppo. What we're observing there is that the Russians, the Iranians and the Syrian government are not working to fight IS, rather the rest of the Syrian rebel groups. This conflict will continue.

Could Turkey weaken the Raqqa offensive? SDF representatives have warned that they might stop their advance if Turkey and its allies were to enter Kurdish regions in northern Syria.

Turkey has already said that it wants to be part of the Raqqa offensive. And it is very likely that Turkey will try to prevent the Kurds from taking control of the city. My assumption is that the US is working hard to stop Turkey from any further intervention in Syria, because it just has the effect of making the situation even more complicated and unpredictable.

What role is the Syrian government playing in efforts to combat IS?

Over the past few years, the Syrian government has had a very clear policy. It has tried to fight mainly the less militant, less Islamist rebels so that in the end, its neighbors, the Europeans, and the Americans have a choice between [Syrian President Bashar] al-Assad's regime and IS - knowing full well that, faced with such a choice, the world would choose Assad. That's why his regime isn't too invested in pushing IS out of Raqqa. And that's why I predict that we'll see lots of things from the Syrian regime that we didn't expect with regard to this operation.

Guido Steinberg is a Middle East and terrorism expert at the German Institute for International and Security Affairs in Berlin. Between 2002 and 2005, he served as an advisor to the chancellor on matters of international terrorism.