In a low, windowless building just outside America's sprawling embassy compound in Baghdad, senior military officials from 19 nations work side-by-side, quietly trying to kill jihadists.

The front wall of the dreary office space is covered by monitors -- many are blacked out as reporters stop by -- that provide live video feeds from the drones and warplanes endlessly circling the skies over large parts of Iraq.

As Iraqi security forces and Kurdish peshmerga units close in on Mosul, US military officials offered a quick glimpse of the Combined Joint Operations Center on Wednesday to highlight how coalition intelligence and air power are helping the Iraqis push the Islamic State group from Iraq.

US military officials repeatedly stress the war is being led by the Iraqis, but without international assistance it's hard to imagine the campaign could have progressed so quickly to this point.

"We advise them based on what they plan and then say yes, we think you should do this, think you should do that," said US Brigadier General Rick Uribe, who must approve every single air strike across parts of Iraq.

"It's their fight, we are supporting them," he said, noting that "they are coming up with the ideas. And we are helping them refine their ideas."

Two years ago, it would have seemed unlikely that Iraqi security forces could now be on the verge of defeating IS in Iraq.

Many Iraqi army units had collapsed in disarray, dumping weapons and equipment, as jihadists swept through the country in 2014, leaving a trail of slaughter and atrocities in their wake.

But a string of victories since the United States pulled together a 60-plus member coalition to help fight IS has helped ensure a string of victories, with each new success bringing experience and confidence to the Iraqi forces.

In the past year, Iraqi troops recaptured Fallujah, a city 50 kilometres (30 miles) west of Baghdad that had been outside government control for more than two and a half years, and Ramadi, the capital of Anbar province.

"Our mission right now and our planning is good. Everything is going like what we (were) planning for it," Iraqi defence ministry spokesman Brigadier General Tahseen Ibrahim said of current anti-IS operations.

While Iraqi military and police are better equipped and trained than they were two years ago, they have also benefitted from more than 10,000 coalition air strikes.

- Gaining confidence -

Inside the Joint Operations Center, one TV that has not been switched off shows a man sprinting across a muddy field, pausing at one moment by a palm tree then stopping a moment later, apparently to dig something from the dirt before running off again.

It's unclear what he is doing, or whether anyone in the room would later deem him a legitimate target for execution via Hellfire missile or coalition bomb.

While total air superiority and technology like this has helped turn the tide for the Iraqi military, training units from the United States, Britain, Italy and other nations have been key on the ground.

Iraqi ground forces are now better drilled in combat skills and discipline. In northern Iraq, the Pentagon has provided peshmerga forces the ammunition and equipment they need to fight IS.

This US tactic of keeping US personnel largely away from the fighting and waging the war by air has garnered broad criticism in the United States, with lawmakers bemoaning an early lack of results and the US public fretting about a perceived growing threat from IS jihadists.

But US leaders and military officials sound increasingly confident IS will soon lose in Iraq.

The jihadist group also has a large footprint in neighbouring Syria, where the coalition is helping train and advise Kurdish fighters who are doing most of the ground combat.

Pentagon chief Ashton Carter on Wednesday said the offensive to push IS from Raqa, their last stronghold in Syria, would begin within weeks.

And late Tuesday, Lieutenant General Stephen Townsend, who heads the coalition effort supporting and training Iraqi security forces and Kurdish peshmerga, said IS would soon be defeated in Mosul.

The jihadists are "living on borrowed time and their clock is running out. The Iraqi security forces are going to take Mosul back, period," he said.