The flag of ISIS flutters over a building in Raqqa, Syria.

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US-backed militia groups said Sunday they had launched an operation to seize the city

Raqqa is ISIS' self-declared capital

CNN  — 

American and Turkish military leaders have agreed to develop a long-term plan for “seizing, holding and governing” the de facto ISIS capital of Raqqa in northern Syria, the US Department of Defense’s news service reported Sunday.

“The coalition and Turkey will work together on the long-term plan for seizing, holding and governing Raqqa,” Chairman of the US Joint Chiefs of Staff Gen. Joseph Dunford said after meeting his Turkish counterpart Army Gen. Hulusi Akar in the Turkish capital Ankara on Sunday, according to DoD News.

Dunford’s visit came after the US-backed Syrian Democratic Forces – which include several Kurdish militant groups that Turkey considers terrorists – announced the launch of their military campaign, “Euphrates Rage,” to seize Raqqa from ISIS. The operation coincides with the coalition campaign in neighboring Iraq to drive the terror group from Mosul, its stronghold in that country.

What to know about the Raqqa offensive

The Syrian Democratic Forces (SDF) said in a statement Sunday they had established a joint operations center for the campaign, which includes multiple Arab, Kurdish and Turkmen militia groups and will be carried out “in coordination with international forces.”

The role of Kurdish forces – one of the most effective forces on the ground against ISIS – in the coalition fighting the terror group has been a source of tension between NATO allies Turkey and the US.

How the ‘Kurdish question’ complicates the anti-ISIS alliance

But DoD News reported that Sunday’s meeting reinforced a longstanding agreement that the US-led coalition would not move ahead with the seizure of Raqqa, “without incorporating the Turks and their perspective into our plans,” according to Dunford.

The Turkish army said in a statement that the military heads had discussed “the methods of a common struggle” against ISIS in Iraq and Syria, “especially in Al Bab and Raqqa in coming days.”

Questions over makeup of forces

Addressing the sensitivities around the ethnic makeup of the forces involved in the operation, Dunford said: “We always knew the SDF wasn’t the solution for holding and governing Raqqa.

“What we are working on right now is to find the right mix of forces for the operation.”

He said the US would work with Turkey to determine the composition of the forces that would seize and govern the territory, he said.

He said the right approach was for locals to lead the mission to retake the city and run it after ISIS was driven out.

“[The operation needs] a predominantly Arab and Sunni Arab force,” he said, according to DoD News. “And there are forces like that. There is the moderate Syrian opposition, the vetted Syrian forces and the Free Syrian Army forces, and there is some initial outreach to forces in Raqqa proper.”

Dunford said the SDF were moving south to isolate ISIS positions in Raqqa and the surrounding areas – a phase that would take months.

This would ensure that ISIS fighters from Mosul could not flee to Raqqa to reinforce the terror group there, and that the ISIS forces in Raqqa could not send out fighters to carry out external attacks in Turkey, Europe and the US, he said, according to DoD News.

Raqqa is home to nearly 200,000 people, most Sunni Arabs, and an estimated 5,000 militants, according to the activist group Raqqa is Being Slaughtered Silently (RSS).

The US and Turkish officials also agreed that a high-ranking US officer and staff will work in Ankara in the Turkish General Staff.

CNN’s Isil Sariyuce contributed to this report.