After nearly securing the Daesh-held city of al-Bab in Syria, Turkish forces will next train their fire on a Kurdish held town, setting up a potential confrontation between a NATO ally and an ethnic group that's proven a stable partner for US-led forces in the region since the 2003 Iraq invasion.

At the crux of the conflict is Turkey's contention that Kurdish forces across its border in northern Syria and Iraq are extensions of a militant Kurdish separatist group that Turkey's government blames for attacks on its soil. Turkey is a member of the North Atlantic Treaty Organization, or NATO, the Western military alliance that has conducted bombing raids on Islamic State targets in Syria and Iraq for years.

US military advisers working closely with regional partners opposed to Daesh in both Iraq and Syria, and have treated the Kurdish soldiers as partners in that effort. The working relationship dates back to the US-led invasion of Iraq, after which Kurdish forces proved able to maintain stability in the northern portion of the country, making them an ally against the Shiite insurgency that followed the invasion.

Turkey, however, takes a very different view of the Kurds and Turkish President Recep Tayyip Erdogan said Friday after Turkish forces finish securing the Daesh-controlled border town of al-Bab in Syria, they would advance their campaign to the city of Manbij, which has been under Kurdish control for more than a year after Kurdish fighters liberated it from Daesh.

Adnan Abu Amjad, the commander of the Syrian Democratic Forces, the name by which the Kurdish forces are known in the region, said his fighters would defend Manbij if Turkey tried to lay siege to the city.

"If Erdogan wants to come to Manbij, it's his business, but we will defend our city with all the strength we can find. As Syrian people, we'll resist any interference in our internal affairs," Amjad said.

Both Syria's Kurds and Syrian President Bashar al-Assad have denounced Turkey's military campaign as a violation of Syria's sovereignty.

The threat from Turkey comes as a top coalition general pointed to the Kurds as potentially playing a key role in the largest fight remaining against Daesh in Syria -- retaking its self-proclaimed capital Raqqa. Coalition forces began meeting in the region Friday to start plotting an offensive that would retake the city from Daesh control. ANA News reported British Maj. Gen. Rupert Jones, the deputy commander of the anti-Islamic State coalition, said the Kurdish SDF, and not the Turkish military, are presently in the best position to mount an offensive to retake Raqqa.

"The force that looks most likely capable of conducting the liberation of Raqqa remains the SDF. Are we confident in the SDF? Absolutely we are," Jones said. "They re-took Manbij, in a very tough fight, and they prevailed in the face of a tough opposition. We've seen their fighting spirit. We've seen what they're capable of doing.

"We've also always said that we would discuss with our partners, in terms of who is best placed to conduct the actual liberation of Raqqa. We'll do that, we'll have those conversations."

By Eric DuVall