Iraqi PM Haider al-Abadi declared the liberation of Mosul from Islamic State (IS) militants as he arrived in Mosul to congratulate Iraqi forces for their victory.

Islamic State militants had occupied Iraq’s second largest city for three years.

Al-Abadi’s media office said he congratulated “the heroic fighters and the Iraqi people for the great victory”. State TV aired scenes of the prime minister’s arrival at the operations command’s office in the city in preparation for a press conference.

Iraqi forces, backed by US-led air strikes, have been battling to retake Mosul since October 17 last year. Islamic State militants seized it in June 2014 before taking much of Iraq's Sunni Arab heartland and proclaiming a "caliphate" straddling Iraq and Syria.

Kurdish Peshmerga fighters, Sunni Arab tribesmen and Shia militiamen have also been involved in the battle.

Iraqi forces have been battling the remaining pockets of jihadists desperately holding out in a tiny area near the Old City.