An Iraqi army offensive touted as the first phase of a campaign to recapture the northern city of Mosul from Islamic State of Iraq and the Levant has been paused until more forces arrive to hold ground, the commander in charge said on Wednesday.

Almost three weeks into the operation, Iraqi forces have retaken just three villages from ISIL, also known as ISIS, in the Makhmour area, which is set to be a key staging ground for a future assault on Mosul, about 60km further north.

The faltering start has cast renewed doubt on the capabilities of the Iraqi army, which partially collapsed when ISIL took about one-third of the country in 2014.

The news came as eight Iraqi forces were killed in an attack launched by ISIL on a military barracks in al-Ma'amel village, east of Fallujah, sources told Al Jazeera.

Major General Najm Abdullah al-Jubbouri, who is in charge of the Makhmour offensive, said Iraqi forces were now waiting for the arrival of federal police units and additional local tribal fighters to hold territory after it is retaken.

Fallujah siege leaves thousands of Iraqis without food

That would free up his forces to go on the offensive against the rebels, Jubbouri said in a statement, dismissing what he described as efforts to disparage the army.

"We do not want to use all our units to hold territory," he said.

The initial target of the latest offensive was Qayara - an ISIL hub on the western bank of the Tigris river - but Iraqi forces have so far failed to recapture the hilltop village of Nasr on the eastern side.

In the statement, Jubbouri said fighters had dug a network of tunnels beneath Nasr and prepared suicide bombers and a fleet of vehicles rigged with explosives, some of which contain weaponised chlorine, a chemical weapon ISIL has used before in northern Iraq.

US Army Major Jon-Paul Depreo, operations officer for the international coalition fighting ISIL in Iraq and neighbouring Syria, said at the weekend the insurgents were determined not to lose Nasr because of its strategic position on high ground.

Depreo also said difficult terrain meant it was not possible to deploy a large number of forces there against fighters, who are more familiar with the area.

"These [Iraqi army] forces aren't from that area necessarily, so they're learning the area," Depreo told reporters in Baghdad.

READ MORE: Wave of ISIL attacks kills 60 in Iraq

The coalition, led by the United States, has trained thousands of Iraqi police and soldiers in preparation for the operation to retake Mosul - by far the largest city in ISIL's self-proclaimed caliphate.

Depreo said the fighting was only one part of the challenge. "There's going to be a lot of fighting but there's also going to be a lot of logistical infrastructure that needs to follow and be established."

Shia militias and Kurdish Peshmerga have played a major role in the fight, but with Mosul the plan is for the army to take the lead to avoid inflaming ethnic and sectarian sensitivities in the mainly Sunni Arab city.

The army won its first major victory over the fighters last December in Ramadi and aims to retake Mosul this year, but Iraqi officials privately question whether that is possible.

"It's a tough fight," Depreo said of the offensive in Makhmour, describing it as a "shaping operation" for the bigger battle ahead. "We have a lot of work to do before we take control of Mosul again."