ERBIL/BAGHDAD (Reuters) - Iraqi forces retook a northern village from Islamic State on Monday, supported by artillery and air strikes from a U.S.-led coalition, as they try to close in on the city of Mosul.

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In March, Iraq’s military opened a new front against the militants in the Makhmour area, which it called the first phase of a wider campaign to liberate Mosul, around 60 km (40 miles) further north. But progress has been slow, and to date Iraqi forces have taken just five villages.

“In a swift operation, our units took the groups of the terrorist organization Daesh by surprise and entered the village,” read a statement from the Nineveh Operations Command, using an Arabic acronym for Islamic State.

A source involved in the operation said the militants put up little resistance in the village of Kabrouk.

The advance brings Iraqi forces slightly closer to the oil town of Qayyara on the western banks of the Tigris River, control of which would help to isolate Mosul from territory the militants hold further south and east.

An air base about 16 km (10 miles) west of the river that U.S. forces used following the 2003 invasion could serve as a staging ground for the Mosul offensive. Kurdish peshmerga forces and a range of militia groups may take part.

The offensive’s faltering start has cast renewed doubt on the capabilities of the Iraqi army, which retreated in disarray when Islamic State seized Mosul in 2014.

Nineveh Operations Commander Major General Najm al-Jabouri blamed the slow pace on a lack of troops. “If it weren’t for the limited units, we could have advanced further, but we don’t have forces to hold ground,” he told Reuters in a recent interview.

His forces had no tanks and were fighting without the elite counter-terrorism forces that have spearheaded most of Iraq’s successful offensives elsewhere, Jabouri said. Islamic State’s use of civilians as human shields has also hampered Iraqi forces.

U.S. Army Colonel Steve Warren, a spokesman for the U.S.-led coalition, said more troops would be deployed to Makhmour and that “tens of thousands” were needed for the final push on Mosul.

“We knew that the fighting would get harder the further north we went and we are seeing that to be the case,” he told Reuters.

Iraqi officials say they will retake Mosul this year. But in private many question whether that is possible. The pace of fighting could slow further as temperatures continue to rise and the month-long Ramadan season begins in early June.