Iraq has finally declared victory over Islamic State in the militants’ stronghold of Mosul after a bloody and devastating nine-month campaign.

Iraqi Prime Minister Haider al-Abadi tweeted on Sunday (local time) that he had arrived in the “liberated city of Mosul” and that he “congratulates the heroic fighters and the Iraqi people in achieving this great victory”.

Mr al-Abadi celebrated with troops after they drove IS fighters from some of their last strongholds in Mosul.

However, Iraqi state television Al-Iraqia TV reported that many IS militants were holding out in one neighbourhood of the Old City of Mosul, with complete victory a matter of hours away.

The victory marks the end of a bloody campaign which began in mid-October last year – almost nine months ago – and which has come at a huge cost.

Mosul, Iraq’s second-largest city, has been left in ruins, killed thousands of people and displaced nearly a million more.

Iraqi forces plant flag on bank of Tigris River as Prime Minister al-Abadi declares victory over ISIS in Mosul https://t.co/Gz1l7aqiQi pic.twitter.com/GvF7HFtVjF

— ABC News (@ABC) July 9, 2017

It was a war of attrition, with IS control of the city being slowly whittled away. Shortly before victory, IS controlled less than one square kilometre of territory in Mosul’s Old City.

But the group used human shields, suicide bombers and snipers in a fight to the death.

The militants captured Mosul, Iraq’s second largest city, in a matter of days in the summer of 2014.

Lieutenant General Jassim Nizal of the Iraqi army acknowledged that many of his men were among those who fled the city at that time in a humiliating defeat for the country’s armed forces.

“Some things happened here, that’s true,” he said. “But we have come back.”

Much of Mosul’s Old City and surrounding areas have been devastated by months of gruelling urban combat.

Destroyed buildings and wrecked cars in Mosul as of July 9. Photo: Getty

On Sunday a line of tired civilians filed out of the Old City on foot, past the carcasses of destroyed apartment blocks lining the cratered roads.

The loss of the city would mark a major defeat for the Islamic State group, which has suffered a series of major setbacks over the past year.

US-backed Syrian forces have pushed into the group’s de facto capital, the northern Syrian city of Raqqa, but a final victory there could be months away, and the extremists still hold several smaller towns and villages across Iraq and Syria.

IS seized Mosul in June 2014 before sweeping across much of Iraq’s Sunni Arab heartland and proclaiming a “caliphate” straddling Iraq and Syria.

But they have been losing ground over the past nine months, as government forces advance on their former Iraqi stronghold.

Kurdish Peshmerga fighters, Sunni Arab tribesmen and Shia militiamen, supported by US-led coalition warplanes and military advisers, have been involved in the battle.

– with agencies