IRBIL, Iraq — Several hundred thousand civilians are enduring desperate conditions and facing retribution by Islamic State fighters in western Mosul as Iraqi forces prepare to attack militants who control the city’s western half, according to residents and humanitarian groups.

In telephone interviews, residents said the Islamic State is using food as a weapon, doling out small amounts to hungry families in return for information gained by spying on neighbors suspected of aiding Iraqi security forces.

They said several residents accused of phoning security forces with information about Islamic State activities had been killed in recent weeks.

Food, water, and fuel for cooking and heating are unavailable or are being sold at prohibitive prices in the area’s densely packed neighborhoods.

Militants have begun hoarding food and supplies while restricting the movements of civilians in anticipation of a government assault, residents said. Stray animals are wandering nearly empty streets.

“We’re no longer afraid of the rockets and the buzzing of bullets — we fear hunger more,’’ said Abu Marwan, a government employee in western Mosul. “Anyone who owns a bag of flour or rice is rich.’’

Like others interviewed, Abu Marwan, citing concerns about safety, agreed to speak on the condition that his full name not be published. He and others are identified by honorifics or nicknames. Residents said anyone caught using a cellphone risked being beaten or killed by militants.

Abu Salah, who lives in the Bab al-Tob neighborhood in western Mosul, said the Islamic State, also known as ISIS, had recruited three families as spies in return for food. He said the families had identified eight young men who were subsequently arrested by militants and accused of providing information to Iraqi security forces.

“We call this food for information,’’ Abu Saleh said. “These are poor families. Hunger pushes them to abandon their principles.’’

The United Nations in Iraq said Saturday that most of the 750,000 to 800,000 residents of western Mosul had been living under extreme duress for weeks, creating a humanitarian crisis even before the start of military operations.

Once the battle for western Mosul begins, a top UN official said, 250,000 to 400,000 people may try to flee. Emergency sites are being built south of Mosul, where food and other supplies are being gathered to accommodate a rush of displaced people.

“Tens of thousands of people may flee or be forced to leave the city,’’ Lise Grande, United Nations’ humanitarian coordinator for Iraq, said in a statement Saturday. “Hundreds of thousands of civilians might be trapped — maybe for weeks, maybe for months.’’

Grande added: “People, right now, are in trouble. We are hearing reports of parents struggling to feed their children and to heat their homes.’’

In Syria on Saturday, US-backed fighters said they had captured a village in the northern part of the country from Islamic State fighters, the Associated Press reported. That brings them closer to cutting a road linking two major cities in the country and closing in on Raqqa, the militant’s defacto capital in Syria.

The Syria Democratic Forces opposition group has been on the offensive toward Raqqa since November.

The Britain-based Syrian Observatory for Human Rights and the SDF said Saturday that the predominantly Kurdish force captured the village of Jawees and is close to cutting the road that the extremists use to travel between Raqqa and the eastern Syrian city of Deir el-Zour.

In Mosul, few, if any, commercial supplies have reached the eastern part of the city in the three months since the main road from that city and Syria was cut, the UN said recently.

With cooking gas and kerosene scarce, families are burning wood, plastic, furniture, and garbage to heat their homes and cook their food.

The United Nations said that most essential food items were virtually unattainable. Half of all food shops have closed, and others have little for sale. Staples like rice, flour, legumes, date syrup, baby formula, and sugar have almost disappeared. There is only enough cooking oil to supply 10 percent of the population.

Umm Aisha, a widow with three children, said her two sons, ages 7 and 5, were weak and listless from hunger. She said her 10-year-old daughter’s face had turned yellow and sunken. “I can’t provide enough food to keep them alive,’’ she said, weeping.

Food prices in western Mosul are almost twice as high as those in eastern Mosul, Sally Haydock, the representative of the World Food Program in Iraq, said in a statement. “We are extremely concerned that many families do not have enough to eat,’’ she said.

The price of a bag of flour has skyrocketed to 150,000 Iraqi dinars, or about $130, said a 41-year-old resident of Bab al-Tob.

The government assault to drive Islamic State fighters from western Mosul, their last stronghold in a major Iraqi city, is expected soon, led by Iraqi troops, supported by US military advisers and firepower.

The recapture of western Mosul would be the climax of a long, bloody slog by the Iraqi military and supporting militias, which have steadily beaten back Islamic State fighters who seized control of one-third of the country in 2014. On Jan. 24, Iraqi forces declared eastern Mosul “liberated’’ after a 100-day battle.