By Ghazwan Hassan

TIKRIT, Iraq (Reuters) – Islamic State has captured most of a village south of Mosul despite losing control of its stronghold in the city, an Iraqi army officer and residents said, deploying guerrilla-style tactics as its self-proclaimed caliphate crumbles.

Prime Minister Haider al-Abadi declared victory over Islamic State in Mosul on Monday, marking the biggest defeat for the hardline Sunni group since its lightning sweep through northern Iraq three years ago.

But the militants, armed with machine guns and mortars, have now seized more than 75 percent of Imam Gharbi, a village on the western bank of the Tigris river some 70 km (44 miles) south of Mosul, and reinforcements are expected, the Iraqi army officer said.

Islamic State launched its attack on Imam Gharbi last week, in the kind of strike it is expected to deploy now as U.S.-backed Iraqi forces regain control over cities the group captured during its shock 2014 offensive.

Mosul resident Hind Mahmoud said by telephone that she had heard exchanges of gunfire in the Old City and seen an Iraqi army helicopter firing on Islamic State militants on Tuesday.

Stripped of Mosul, Islamic State’s dominion in Iraq will be reduced to mainly rural, desert areas west and south of the city.

Islamic State also faces pressure in its operational base in the Syrian city of Raqqa, where U.S.-backed Syrian Kurdish and Arab forces have seized territory on three sides of the city.

The campaign to retake Mosul from the militants was launched last October by a 100,000-strong alliance of Iraqi government units, Kurdish Peshmerga fighters and Shi’ite militias, with a U.S.-led coalition providing key air and ground support.

Abadi’s government in Iraq now faces a difficult task managing the sectarian tensions which enabled Islamic State to gain supporters in the country among fellow Sunnis, who say they were marginalized by the Shi’ite-led government.

The U.S.-led coalition warned that victory in Mosul did not mark the end of the group’s global threat.

“Now it is time for all Iraqis to unite to ensure ISIS (Islamic State) is defeated across the rest of Iraq and that the conditions that led to the rise of ISIS in Iraq are not allowed to return again,” Lieutenant General Stephen J. Townsend said in a statement.

(Writing by Michael Georgy; Editing by Gareth Jones)