An Iraqi operation to recapture the city of Mosul, the last stronghold of the so-called Islamic State (IS) in the country, has started. Artillery began firing on the city early on Monday, in a long-awaited assault from Kurdish Peshmerga, Iraqi government and allied forces. Tanks are now moving towards the city, which has been held by IS since 2014.

The UN has expressed "extreme concern" for the safety of up to 1.5 million people in the area. The BBC's Orla Guerin, who is with the forces, says Kurdish tanks are advancing on Mosul, kicking up clouds of dust.

As the operation began, one Kurdish general said: "If I am killed today I will die happy because I have done something for my people." The recapture of the city, officials say, would mark the effective defeat of IS in Iraq.

The start of the operation was announced by Prime Minister Haider al-Abadi in an televised address in the early hours of Monday (local time), "The hour of victory has come," he said.

"Today I declare the start of the heroic operations to liberate you from Daesh," he said, using another name for IS.

"God willing we will meet in Mosul to celebrate the liberation and your salvation from Isis (IS) so we can live together once again, all religions united and together we shall defeat Daesh to rebuild this dear city of Mosul."

Surrounded by senior Iraqi officers, he vowed that only government forces would enter Mosul, a Sunni-majority city.

This, analysts said, was an attempt to counter fears that the operation could turn into a sectarian conflict.

US Secretary of Defence Ash Carter described it as "a decisive moment" in the campaign to deliver IS "a lasting defeat". But he added that it would be a "difficult fight".