A major battle to recapture Mosul, the capital of so-called Islamic State, from militant fighters has begun.

Iraq's Prime Minister Haider al-Abadi launched the offensive to liberate the city after "two years of darkness" on Sunday.

Mosul, which had a population of over two million people before its capture, fell to so-called Islamic State in June 2014.

On Sunday, Prime Minister al-Abadi announced on state TV: "The time has come for the greatest victory".

After the announcement, the United States said it was proud to stand with the Kurdish Peshmerga and Iraqi government forces.

Brett McGurk, the US envoy to the coalition against IS, confirmed the offensive's launch on Twitter.

"PM Abadi issued orders to initiate major operations to liberate Mosul after two years of darkness under ISIL terrorists", he wrote.

US Secretary of Defence Ash Carter said he hoped the campaign would deal so-called Islamic State a "lasting defeat".

He added that the US was willing to support Iraqi forces in the "difficult fight ahead".

Mosul is so-called Islamic State's last major stronghold in Iraq.

Last month, Defence Secretary Michael Fallon revealed that British troops would take part in a massive offensive to retake Mosul.

Mr Fallon said the city would become "encircled" as the operation attempts to wrest control of the remaining 10% of Iraq still controlled by the terror group.

"This is the final battle," Mr Fallon told ITV News.

The UN has warned that the fighting could have an "enormous" humanitarian impact on the city.

Leaflets were dropped in Mosul telling people to prepare for the assault.