Iraq’s Prime Minister Haider al-Abadi has announced “victory” over the Islamic State of Iraq and the Levant (ISIL) group in the city of Mosul, according to his office.

“The commander in chief of the armed forces Haider al-Abadi arrived in the liberated city of Mosul and congratulated the heroic fighters and the Iraqi people for the great victory,” said a statement from his office on Sunday.

Photographs released by his office showed the premier dressed in a black military uniform and cap, shaking hands with police and army officers as he arrived in the city.

The victory announcement came after state TV reported that troops had reached the Tigris riverside and raised the Iraqi flag there.

The operation has been backed by a US-led coalition battling ISIL in Syria and Iraq, which has carried out waves of air strikes against the group and deployed military advisers on the ground.

Emmanuel Macron, the president of France, whose country is a key part of the coalition, was among the first world leaders to offer his congratulations.

“Mosul liberated from Daesh,” he tweeted, using an Arabic acronym for ISIL. “Homage from France to all those, with our troops, who contributed to this victory.”

About 100 ISIL fighters had earlier been reported to be trapped in a sliver of the Old City along the Tigris.

Many of them threw themselves into the river earlier on Sunday as they faced imminent defeat, according to Reuters news agency.

The agency also reported plumes of smoke over the Old City and decaying corpses of ISIL fighters lying on its streets.

Scattered bursts of gunfire could be heard and several air strikes were carried out, it said.

The fall of Mosul would be the biggest defeat yet for ISIL three years after it seized the city in a lightning offensive.

With air support by the US-led coalition, Iraqi forces launched the battle for Mosul in October, retaking the eastern part of the city in January and starting the operation for its western part the next month.

The nearly nine-month battle for Mosul has ruined parts of the city, killed thousands of civilians and displaced nearly one million people.