The United States hailed the retaking of the Iraqi city of Mosul Monday, calling it a "critical milestone" in the fight against the Islamic State group.

"On behalf of President Trump and the American people, I congratulate Prime Minister Abadi and the Iraqi people on their liberation of Mosul," US Secretary of State Rex Tillerson said.

"This is a critical milestone in the global fight against ISIS, and underscores the success of the international effort led by the Iraqi Security Forces," he said.