Islamic State militants overran Mosul, a city of more than one million people, in June 2014, but a much anticipated counter-offensive by Iraqi forces has been repeatedly postponed because they are involved in fighting elsewhere.

"Turkish soldiers have reached the Mosul Bashiqa region. They are there as part of routine training exercises. One battalion has crossed into the region," the source said, declining to say exactly how many soldiers had been deployed.

Video released on the website of Turkey's pro-government Yeni Safak newspaper showed flatbed trucks carrying armoured vehicles along a road at night, describing them as a convoy accompanying the Turkish troops to Bashiqa.

In Washington, two US defence officials said that the United States was aware of Turkey's deployment of hundreds of Turkish soldiers to northern Iraq but that the move is not part of the US-led coalition's activities.

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