BEIRUT – U.S.-backed Syrian forces on Sunday said they would march on the northern city of Raqqa, the de facto capital of the Islamic State group's self-styled caliphate.
The offensive promises to divert IS fighters from Mosul, the much larger extremist-held city in northern Iraq, which has been the target of a massive operation launched by Baghdad last month. But long-running tensions between Turkey and the Syrian Kurdish-led forces leading the assault on Raqqa could complicate the battle and buy IS more time.
A closer look at what the new offensive means:
WHO IS LEADING THE OFFENSIVE?
The Kurdish-dominated Syria Democratic Forces have emerged as one of the principal players in the country's multi-sided civil war. They are recognized by the U.S. as one of the most effective fighting forces against IS and have captured large swaths of northeastern Syria from the extremists.
The force is dominated by the Kurdish Party of Democratic Unity, or PYD, which aims to defend Kurdish areas of Syria. Despite occasional flare-ups, the PYD has had a tacit non-aggression pact with the Syrian government since the start of the civil war, and is seen by some rebels as a quiet ally of President Bashar Assad, accusations the PYD denies.
WHY MIGHT TURKEY OBJECT?
Turkey views the PYD as an extension of the Kurdish insurgency raging in its southeast, and often speaks of the PYD and IS as similar threats.
Turkish forces and thousands of allied Syrian opposition fighters launched their own offensive in northern Syria earlier this year, clashing with both the PYD and IS. Turkish President Recep Tayyip Erdogan has suggested his own forces and allies should liberate Raqqa, and has also demanded a greater role in Mosul, angering Iraq.
The U.S. wants all of its allies to set aside their grievances, at least temporarily, and focus on IS, but a series of visits by top officials in recent weeks has yielded no major breakthroughs. Turkey has yet to comment publicly on the Raqqa offensive.
HOW SOON UNTIL RAQQA IS FREED FROM IS?
The Raqqa offensive is likely to take months, and the SDF has said the early stages will focus on sweeping the countryside on its outskirts and gradually isolating the city.
The SDF says it has 30,000 fighters assigned to the campaign, but senior SDF officials have warned progress would be halted if Turkey and its allies advance on other Kurdish-held territory.
If Mosul is any indication, the battle for Raqqa will be a long and grinding one. Nearly three weeks after launching the long-awaited push on Mosul, Iraqi forces have only entered the eastern edge of the city, and have met with stiff resistance in the form of suicide car bombs, rocket attacks and booby-trapped buildings.
WOULD THE LOSS OF RAQQA MEAN THE END OF IS?
The loss of Raqqa would deal a major blow to the extremist group.
Raqqa is the seat of power for its self-described caliphate and is likely home to top IS leaders. It is also where the militants are believed to have plotted attacks on Western nations, including last year's assault on Paris.
But IS has already begun preparing its followers for the potential loss of territory, and if it is driven from Raqqa and Mosul it will likely return to its insurgent roots. As forces close in on the two cities, many fighters are expected to melt into the civilian population, with some forming so-called "sleeper cells" that could hatch new attacks.
WHAT ABOUT SYRIA'S CIVIL WAR?
The war between Syrian President Bashar Assad and the rebels fighting to unseat him is centered on the divided northern city of Aleppo, where IS has no presence.
The government and its ally Russia have vowed to launch a new push to retake eastern Aleppo, held by the rebels since 2012. If that succeeds, it would free up thousands of government forces that could be sent to other fronts, perhaps to battle IS.
But since the start of the conflict, Assad and his allies have been more focused on battling Syrian rebels, who are concentrated in the country's main cities in the west, than the Islamic State group. That's unlikely to change, especially if other forces are willing to battle the extremists.