Mosul (Iraq) - Islamic State (ISIS) 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 ISIS in Mosul on Monday, marking the biggest defeat for the terrorist 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. ISIS launched its attack on Imam Gharbi last week, in the kind of strike it is expected to deploy now as Iraqi forces regain control over cities the group captured during its shock 2014 offensive. Daesh 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. Abadi's government in Iraq now faces a difficult task managing the sectarian tensions which enabled ISIS to gain supporters in the country. 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 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.