Iraqi Prime Minister Haider al-Abadi (C) declares victory of Mosul battles against IS group on July 9. (Reuters Photo)

MOSUL, Iraq, July 9 (Xinhua) -- Iraqi Prime Minister Haider al-Abadi arrived in Mosul on Sunday and congratulated the armed forces for their victory over Islamic State after 266 days of battles, liberating Mosul from IS after its three years of rule in the city.

Liberating Mosul from the occupation of Islamic State (IS) is a great victory for Iraq's anti-terror war, but the war-torn country will face grave challenges of national reconstruction and reconciliation, experts said.

Iraqi forces have liberated Mosul, the capital city of Iraq's northern province of Nineveh and the second largest Iraqi city, after a nine-month fierce battle to drive out IS, which had used the city as its de facto capital.

It was in Mosul that IS leader Sheikh Abu Bakr al-Baghdadi declared in 2014 the establishment of Islamic State (IS), a caliphate in Iraq and Syria. The fall of Mosul symbolizes the total collapse of IS in Iraq.