The Obama administration June 23 touted Kurdish-led advances against the Islamic State in Syria as a model for efforts in Iraq to retake territory from the militant group.
Kurdish forces in the past week have seized a Syrian military base and a key Turkish border town that was a conduit for supplies and foreign fighters for IS. They are now retaking territory close to Raqqa, IS's power center, with Kurdish forces June 23 capturing the town of Ein Issa, which is only 50 kilometers from Raqqa.
The recent blows to IS, which was achieved with the aid of U.S. air strikes and intelligence sharing, contrasts with the successes the militants have met with in other parts of Syria and Iraq, where the key western city of Ramadi fell to IS this spring after Iraqi troops abandoned their defense of the town.
The advances by Kurdish fighters in northern Iraq as well as Syria have been credited largely to a high level of coordination between the ground forces and the nearly year-old air campaign led by Washington.
"This is, I think, an indication of how critically important it is for the United States to have a capable, willing and effective partner fighting ISIL on the ground," White House spokesman Josh Earnest said, in a pointed reference to concerns among U.S. military leaders about the willingness of troops in Iraq to fight IS.
Earnest credited the Kurdish gains in part to Washington having convinced Ankara last year to allow Iraqi Kurdish peshmerga fighters armed by the United States to cross Turkish territory to help Syrian Kurds retake the border town of Kobani, in a key defeat for IS.
While Kurds have united into a strong force against IS both in Syria and northern Iraq, Washington faces a formidable challenge in the rest of Iraq where it must try to meld rival Shi'ite and Sunni Arabs into a fighting force, with Iranian fighters and advisers thrown into the mix.
The United States is dedicating "significant resources" to building up Iraqi forces, which has been a "difficult task," Earnest said. The better outcomes in Kurdish areas "is a pretty good illustration of why that very difficult work is important."
The Pentagon and Kurdish spokemen declined to say whether Raqqa might be their next target.
"We're not going to say specifically what our immediate plans are. Obviously our ultimate objective is to expel ISIL completely," said Army Colonel Steve Warren, a Pentagon spokesman.
U.S. officials cautioned that Kurdish forces will need time to consolidate their gains, and they point out that IS has a proven track record of adapting and quickly recovering from setbacks.
"ISIL has proven a resilient force," a U.S. intelligence source told Reuters. "In the past, it has sought to offset losses with attacks elsewhere."
Warren said the Kurdish fighters' seizure of a northwest highway between Raqqa and the Turkish border would make it harder for IS to keep up the flow of arms and foreign fighters into the heart of the territory it holds.
But U.S. officials said the militant group has other supply routes and is not at immediate risk of being cut off.