The battle started just after dawn local time with a bulldozer, then a truck bomb. And it ended with a US Navy Seal dying at a Kurdish Peshmerga outpost on the outskirts of Mosul, Iraq.

About 125 Isis (Islamic State) fighters surprised a handful of US military advisers holding a meeting with the Peshmerga a few kilometres outside the Isis-held city, touching off a day-long fight which included US helicopters, a commando quick reaction force, and warplanes dropping dozens of bombs to push the insurgents back.

Today, the Pentagon provided new details of the Wednesday strike that killed Special Warfare Operator 1st Class Charles Keating IV - the third American killed in Iraq since October. It was a sobering reminder of just how close US forces are to the front lines in the upcoming battle for Mosul, which fell to Isis in June 2014.

The fight took place near the town of Tal Asqaf, and minutes after the truck bomb detonated, the Americans called for help.

Advertisement
Advertise with NZME.

That's when the quick reaction force - which included Keating - arrived, fighting their way in, and then fighting on their way back out. Keating was killed as the Americans were pulling out, said Army Colonel Steve Warren, the US military's spokesman in Baghdad.

Intense ground fire also hit, and damaged, two US helicopters. After the US troops left, the Peshmerga and Isis fought it out until late into the evening, with the insurgents eventually pulling back. But 11 different US Air Force jets - including a B-52 - pounded the Isis fighters with 31 airstrikes, destroying many of the insurgent's vehicles and, Warren said, along with two more truck bombs on their way to the battle.

Keating's death comes just after Defence Secretary Ash Carter announced the deployment of 217 more troops to Iraq - adding to the 5000 already there - and bringing the US military's footprint in Syria to 300 ground forces.

The role of US troops in the fight remains somewhat murky, though special operations forces in Iraq have launched a series of kill-or-capture missions against Isis leadership over the past several months.

When US troops were sent back to Iraq in June 2014 to train and advise local forces, Defence officials insisted they would mostly remain on large bases, well away from the fighting. But new plans call for American advisers to push closer to the front lines while embedding with Iraqi army battalions to help direct the fighting.

The prize - in Iraq at least - is the city of Mosul, which fell to Isis in June 2014. US warplanes have been targeting Isis in and around the city for months as Kurdish and Iraqi forces push forward on the ground in hopes of cutting off key supply routes between Mosul and the Isis stronghold in Raqqa, Syria.

Over the past two years, American forces have retrained about 21,000 Iraqi and Kurdish forces after the Iraqi Army all but collapsed in the face of the Isis assault across the country's north and west. US officials have estimated that it would take at least 20,000 troops, backed up by US airpower, to retake Mosul, but American and Iraqi officials have yet to launch their campaign. Several thousand Iraqi troops and their US advisers have been massing near the town of Makhmour southeast of the city, and are slowly, if not always successfully, clearing the countryside.

Joint Chiefs of Staff Chairman Joseph Dunford told Foreign Policy earlier this week that Iraqi Prime Minister Haider al-Abadi - who is fighting for his political life in Baghdad - has been holding discussions with Kurdish and Iraqi leaders as well as US officials about planned military operations to take back the city.

"It was moving in the right direction as of Friday, and we'll have to see what happens this week," Dunford said. But real questions remain over what kind of political power-sharing arrangements will be possible in Mosul, an ethnically-mixed city. "It's less about the operation going forward and what's going to happen the day after," he said.

- Foreign Policy