BAGHDAD/ERBIL, Iraq (Reuters) - Iraq’s armed forces went on the offensive against Islamic State in the northern province of Nineveh on Thursday in what Prime Minister Haider al-Abadi described as the first phase of a campaign to liberate areas around the city of Mosul.

Slideshow ( 4 images )

The assault was launched from the Makhmour area, to which thousands of Iraqi troops have deployed in recent weeks, setting up base alongside Kurdish peshmerga and U.S. forces around 60 km south of Mosul, Islamic State’s main bastion.

Iraqi officials say they will retake Mosul this year but, in private, many question whether the army, which partially collapsed when Islamic State overran a third of the country in June 2014, will be ready in time.

The northern city is by far the largest population center controlled by the jihadists, and has already been cut off on three sides by the peshmerga, who are less than 15 km (9 miles) from its northern outskirts at some points along the front line.

Backed by air power from a U.S.-led coalition of Western and Arab states, and by the peshmerga, Iraqi troops advanced westwards at dawn, recapturing several villages from the militants, according to multiple military sources.

Abadi said the move had been “swift and decisive”.

“Daesh is in retreat,” he tweeted, using a derogatory Arabic acronym for the group.

Peshmerga commander Najat Ali said Iraqi forces had taken a couple of villages without any resistance but that Islamic State was putting up a fight in two others, and had set oil ablaze to produce smoke as a shield against coalition air strikes.

A contingent of local Sunni tribal fighters also took part in Thursday’s offensive, which brings Iraqi forces closer to the Tigris river.

Iraqi security analyst Hisham al-Hashimi said it remained to be seen whether troops would be able to cross over to the oil town of Qayara on its western bank.

Qayara is an Islamic State hub connecting Mosul with their stronghold of Hawija further east, from which the militants have threatened oil installations around Kirkuk.

A Shi’ite militia leader met Kurdish peshmerga commanders last week to discuss plans to push the insurgents out of the Hawija area together with the Iraqi army.

A military statement cited by Iraqi state TV said Thursday’s advance was the first phase in an operation dubbed “Fatah”, or “Conquest”, that aimed to liberate Nineveh province, of which Mosul is the capital.

The military statement urged civilians to stay away from buildings used by the insurgents, warning that they would be targeted in days to come.