Iraqi state television says Prime Minister Haider al-Abadi has announced the start of operations to liberate the northern city of Mosul from Islamic State militants.

State TV showed a brief written statement in the early hours Monday announcing the start of the widely anticipated military offensive to drive IS out of Iraq's second largest city.

The push to retake Mosul will be the biggest military operation in Iraq since American troops left in 2011 and, if successful, the strongest blow yet to the Islamic State.