webBAGHDAD: Iraqi government forces, with air and ground support from the US-led coalition, launched an offensive on Monday to drive Daesh from the city of Mosul, the militants’ last major stronghold in the country.

The assault on the northern city was the biggest operation mounted by the Iraqi military since U.S. forces withdrew in 2011, and the United States predicted Daesh would suffer “a lasting defeat.”

As the assault got underway, a Reuters correspondent saw helicopters overhead releasing flares and heard explosions on the city’s eastern front, where Kurdish fighters moved forward to take outlying villages.

Some 30,000 troops from the Iraqi army, Kurdish Peshmerga militia and tribal fighters were expected to take part in the offensive to drive an estimated 4,000 to 8,000 Daesh militants from Mosul.

“I announce today the start of the heroic operations to free you from the terror and the oppression of Daesh,” Prime Minister Haider Abadi said in a speech on state TV, using an Arabic acronym for Islamic State.

“We will meet soon on the ground of Mosul to celebrate liberation and your salvation,” he said, surrounded by the armed forces’ top commanders.

Qatar-based al-Jazeera television aired video of what it said was a bombardment of Mosul that started after Abadi’s speech, showing rockets and bursts of tracer bullets across the night sky and loud sounds of gunfire.

The assault on Mosul, a city of 1.5 million people, is the biggest undertaken by the Iraqi military since 2011 and could be one of the biggest military operations in Iraq since the 2003 U.S.-led invasion that toppled Saddam Hussein.

“This operation to regain control of Iraq’s second-largest city will likely continue for weeks, possibly longer,” said the commander of the coalition, U.S. Lt. Gen. Stephen Townsend, in a statement.

Mosul is the largest city that Daesh controls and its last major stronghold in Iraq.

“This is a decisive moment in the campaign to deliver ISIL a lasting defeat,” U.S. Defense Secretary Ash Carter said in a statement, using an acronym for Daesh.

“We are confident our Iraqi partners will prevail against our common enemy and free Mosul and the rest of Iraq from ISIL’s hatred and brutality.”

In 2014, Daesh leader Abu Bakr al-Baghdadi proclaimed from Mosul’s Grand Mosque a “caliphate” in Iraq and neighboring Syria.