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Iraq’s prime minister on Sunday announced an offensive to seize control of western Mosul from the terror group ISIS.

Iraqi Prime Minister Haider al-Abadi said on state television Sunday morning that the new push has begun. Hours earlier, Iraq’s military said planes dropped leaflets into the area, urging those who joined ISIS to surrender, and warning that the military would move into the western coast of the city, which straddles the Tigris River.

"I announce today the start of military offensive to liberate the western coast of Mosul," al-Abadi said. He added, "our mission is to liberate people before land."

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ISIS seized control of the northern city in 2014, and Iraqi forces entered the city for the first time since then in November. Mosul has been called ISIS’ capital in Iraq, although its stronghold is in the Syrian city of Raqqa.

"The battle for the complete liberation of Mosul cannot come soon enough for the hundreds of thousands of Iraqi citizens who for more than two years have suffered under ISIS oppression in West Mosul, during which time ISIS committed horrible atrocities and terrorized the people of Mosul," said a statement from the Combined Joint Task Force — a U.S.-led international coalition.

“ISIS’s cruelty, brutality and reach show they are not just a threat in Iraq and Syria, but to the region and the entire world,” said Lt. Gen. Stephen Townsend, commander of the task force's Operation Inherent Resolve.

Related: Discarded ISIS Receipts Offer Glimpse into Life in Mosul

The Iraqi military, backed by the U.S. and other Western allies, have effectively surrounded the city. There are an estimated 750,000 civilians in the western section of the city, according to the United Nations and other groups.

The United Nations Office for the Coordination of Humanitarian Affairs said Saturday that the situation for civilians trapped there is dire, as a road to Syria has been cut off and food and fuel supplies have dwindled.

"People, right now, are in trouble. We are hearing reports of parents struggling to feed their children and to heat their homes,” Lise Grande, the Humanitarian Coordinator for Iraq, said in a statement.

Related: Mosul Bridges Are Key to Liberating ISIS Stronghold

The agency was readying to prepare to distribute supplies, warning that tens of thousands of people may flee or be forced to leave the city during the military campaign.

"We don't know what will happen during the military campaign but we have to be ready for all scenarios. Tens of thousands of people may flee or be forced to leave the city. Hundreds of thousands of civilians might be trapped — maybe for weeks, maybe for months,�" Grande said.