Why is Iraq's Mosul dam so important?

There are conflicting reports about whether Kurdish Peshmerga fighters and Iraqi troops have fully retaken Mosul dam from Islamic State (IS) militants.

Iraqi military spokesman Lt-Gen Qassim Atta told state TV the dam - Iraq's largest - had been "fully cleansed".

Troops had been backed by a joint air patrol, he added, without specifying if there had been any US air strikes.

However, journalists in the area said fighting was continuing and jihadists remained in control of the main gate.

Jim Muir reports.