Army Lieutenant General Stephen Townsend also said in a news briefing that the U.S.-led coalition fighting Islamic State wished to move urgently to isolate Raqqa because of concerns about the group using the city – its main stronghold in Syria – as a base to plan and launch attacks against targets abroad.
The United States regards the YPG as an ally in its fight against Islamic State, but Turkey regards it as a terrorist organization because of its links with ethnic Kurdish militants involved in a three-decade insurgency within Turkey.
Kurdish militia groups have played a large role over the past year in the Syrian Democratic Forces (SDF), a U.S.-backed umbrella group, as it has seized large areas of territory from Islamic State, laying the groundwork for an assault on Raqqa.
Townsend added that intelligence officials believe that Islamic State is using Raqqa as a central planning point for international attacks.
“The only force that is capable on any near-term timeline are the Syrian Democratic Forces, of which the YPG are a significant portion,” Townsend said. “We’re going to take the force that we have and we will go to Raqqa soon with that force.”
“We think it’s very important to get isolation in place around Raqqa to start controlling that environment on a pretty short timeline,” he noted.
But Arab forces, and not Kurdish ones, are expected to be the ones to take the city itself, U.S. officials say.
U.S. Defense Secretary Ash Carter has repeatedly signalled this week that the campaign in Raqqa was fast approaching, telling reporters travelling with him in Brussels on Wednesday that the start of the operation was weeks away.
“I think it will be within weeks, that’s what I want to say, and not many weeks,” Carter said, adding the goal was to generate and position local forces to start isolating the city.
“We’ll have fewer coalition troops there, less combat capability there, we’ll have to apply coalition combat support in a different way then we are doing here in Iraq,” he said.
There will be efforts to recruit and train forces local to Raqqa, with much of the training being carried out by local partners, Townsend said, adding that the training would likely be undertaken in northern Syria.