As Iraqi and Kurdish forces launch a military operation to retake the city of Mosul from the so-called Islamic State (Isis), broadcasters are streaming the battle live on Facebook.

The operation, announced by Iraqi prime minister Haider al-Abadi on state TV, aims to free Iraq's second largest city and will be backed by US-led airstrikes.

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The United Nations has warned of the humanitarian crisis that military action would bring.

In perhaps a first for wartime media coverage, news channels have streamed the ongoing battle live on Facebook. Doha-based state-funded Al-Jazeera and Channel 4 in the UK are among those sharing a live feed from the Kurdish media group, Rudaw.

Just like any other Facebook lives, users are able to comment or leave an emoticon on the feed.

Some people have been baffled by the notion of live streaming war on social media:

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Media organisations have used Facebook live to report on protests and demonstrations before, notably in Charlotte.

Mosul, Iraq's second largest city, fell to IS in the summer of 2014. Weeks later the head of the extremist group, Abu Bakr al-Baghdadi, announced the formation of a self-styled caliphate from the pulpit of one of its mosques.

Iraqi president al-Abadi said: "These forces that are liberating you today, they have one goal in Mosul which is to get rid of Daesh and to secure your dignity. God willing, we shall win."

The Associated Press contributed reporting.