US allies are ready to send roughly 1,500 security personnel to Iraq to help the Baghdad government in its fight against jihadists, the American commander of the war effort said Monday.

The move reflects a widening international campaign against the Islamic State (IS) group in Syria and Iraq, and follows Washington's decision to double its military footprint to 3,100 troops.

Members of the US-led coalition meeting last week in the region made initial pledges that would bring "close" to 1,500 forces to Iraq to train and assist the country's army, in addition to the Americans already mobilised, Lieutenant General James Terry told reporters in Kuwait City.

The US general did not indicate which countries from the coalition would provide the security personnel or how many of them would be in uniform or otherwise.

Terry said he was encouraged by the results of the December 2-3 gathering of coalition representatives, with allies eager to send trainers.

"When you start now to balance the different capabilities out across the coalition, I think we're doing pretty well in terms of boots on the ground," Terry told reporters travelling with Pentagon chief Chuck Hagel.

But the details of the contributions were still being discussed.

"We're still working through it," he said. "I want to give them time to go back to their nations' capitals and work out the specifics of that."

He said "the large percentage" of the personnel to be deployed would be training Iraqi troops.

The coalition of mainly Western and Arab states was set up after IS jihadists swept across northern Iraq, seizing swathes of territory and proclaiming a caliphate in parts of the country and neighbouring Syria.

- Militants on defence -

There are already about 1,500 US troops in Iraq providing security for the American embassy and advising the Baghdad government's army and Kurdish forces.

Last month President Barack Obama approved the deployment of another 1,500 to bolster the training and advising effort across the country.

Terry, who oversees the war against the IS group, said Iraqi security forces were steadily improving but remained months away from staging large-scale offensives that could roll back the militants.

"While they still have a long way to go I think they're becoming more capable every day," he said.

The IS group meanwhile faces daily air strikes from US and coalition aircraft that have limited the fighters' mobility and disrupted sanctuaries in Syria, according to Terry.

The militants are "on the defence, trying to hold what they had gained but still able to conduct some limited attacks out there."

The result was a stalemate on the battlefield in some areas, including western Anbar province, he said.

"In some places it's stalemated and some places it's to the advantage of the Iraqi security forces," Terry said.

US and allied warplanes kept up a bombing campaign over the weekend, with 15 strikes in Syria and 31 across Iraq since Friday, the American military said in a statement.

After more than 1,200 air strikes against the jihadists in Iraq and Syria since August 8, the Islamic State group is "starting to feel pressure," Terry said.

"The effect it's having right now is ISIL is having a hard time in movement, having a hard time with communications, and they're having a hard time in governing these populations," he added, using another acronym for IS.

- 'New momentum' -

The general's remarks echoed comments earlier by Pentagon chief Chuck Hagel, who said Iraqi government troops were increasingly taking the fight to the jihadists.

Air power and other support from the US-led coalition "has in effect allowed the Iraqi security forces to take back some ground," Hagel said during a visit to a US base in Kuwait.

"It's given them some new momentum, organisation, structure."

Hagel spoke to reporters during a visit to Camp Buehring, about 40 kilometres (25 miles) from the Iraqi border.

During the 2003-2008 US occupation of Iraq, most American troops passed through the outpost in Kuwaiti to get acclimatised to the desert.

The base now serves as the headquarters for US forces in Iraq, officials said.