Kurdish YPG will be part of efforts to isolate Raqqa: US commander

Kurdish YPG militia fighters will be a part of the force to isolate the Islamic State-held Syrian city of Raqqa, the top US military commander in Iraq said on Wednesday.

Army Lieutenant General Stephen Townsend also said in a news briefing that the US-led coalition fighting IS 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 IS, but Turkey regards it as a terrorist organisation 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 US-backed umbrella group, as it has seized large areas of territory from IS, laying the ground for an assault on Raqqa.

"Turkey doesn't want to see us operating with the SDF anywhere, particularly in Raqqa," Townsend said. "We're having talks with Turkey and we're going to take this in steps."

Townsend added that intelligence officials believe that IS 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 said.

US Defence 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 that the goal was to generate and position local forces to start isolating the city.

Carter said on Tuesday the attack on Raqqa would start while the battle of Mosul in neighbouring Iraq is still unfolding.