Pentagon chief urges joint Raqqa and Mosul assaults

US defence chief Ashton Carter, in Iraq for a second day, said on Sunday that an operation to isolate the Islamic State (IS) group in Syria's Raqqa should begin in conjunction with the assault on the militants' Iraqi bastion Mosul.

"We want to see an isolation operation begin around Raqqa as soon as possible," Carter said during a visit to Iraq's autonomous region of Kurdistan to review an ongoing offensive to retake Mosul from IS.

"We are working with our partners there [in Syria] to do that," the US secretary of defence said, adding: "There will be some simultaneity to these two operations."

Carter met Kurdish leader Massoud Barzani, as well as US service members, who are not far from the battle. The Pentagon chief said Barzani reported some good news about Peshmerga gains against IS in taking the fortified village of Bashiqa, northeast of Mosul.

Iraqi forces launched a huge operation last week to retake Mosul, the last major city in Iraq under IS control.

The US leads a 60-nation coalition that has provided key support in the form of thousands of air strikes, training to Iraqi forces and advisers on the ground.

The loss of Mosul would leave Raqqa - the de facto capital of the militants self-declared "caliphate" - the only major city still under IS control.

Carter said the idea of simultaneous operations against Mosul and Raqqa "has been part of our planning for quite a while".

He also warned that it was necessary to prepare to rebuild Iraq’s second-biggest city.

"We need to make sure that the non-military campaign doesn't lag behind the coalition," said Carter, who added that he's "encouraged by the progress" of the military campaign. "My mind is already thinking ahead to the desperate need for stabilisation and reconstruction."

He said that destroying IS's external operations capabilities was "our highest priority".

"We are getting better and better and better at that.

"Mosul will help us with that, even as all the other territories we have taken."

The gathering of more intelligence information would also provide "new opportunities to attack external plotters," Carter said.

In Iraq, the coalition is allied with both federal forces and Kurdish Peshmerga fighters in the Mosul battle.

But in Syria, the issue of which ground forces would be involved in an operation to retake Raqqa would be far more complicated.

The US has given support to Syrian rebels and the Kurdish-led Syrian Democratic Forces who have battled IS.

But President Bashar al-Assad's forces, backed by Russia and Iran, are also fighting IS.