Davis said the operation to retake Mosul will be "an ugly fight".
Why has this Government chosen to give priority to people who have travelled through many safe European Union countries to camp in the lawless Jungle in Calais - many break the law to try to get to the United Kingdom - when we don't know if they are victims of war?
The northern city was where IS supremo Abu Bakr al-Baghdadi publicly proclaimed a "caliphate" straddling Iraq and Syria in June 2014.
The ministry said in light of the recent offensive to re-take Mosul, Iraq's general security situation would deteriorate and cause acts targeting Turkey's interests in the country.
So far in the first 48 hours of the military operation, Iraqi forces have seen less resistance outside the city.
Davis also said U.S. Apache helicopters - which could provide close air support for Iraqi and American forces - were "ready" to be used but have not been used yet.
In a previously undisclosed incident, US forces confirmed the presence of a sulfur mustard agent on Islamic State munition fragments on October 5, a second official said.
He warns that with more than 3 million people already displaced in Iraq, officials would struggle to cope with the exodus.
The Peshmerga, who are also deployed north and northwest of the city, said they secured "a significant stretch" of the 80 km (50 mile) road between Erbil, their capital, and Mosul, about an hour's drive to the west.
While the Pentagon has said publically that more than 100 US special operations forces are embedded with Iraqi counter terrorism service (CTS) and Kurdish peshmerga fighters, Fox News is told that number is much higher - upwards of 300.
The military campaign could last weeks, officials predict.
Coalition warplanes attacked 17 Islamic State positions in support of the Peshmerga operation in the heavily mined area, the Kurdish statement said, adding that at least four auto bombs were destroyed.
The plan is for the Kurds not to enter Mosul itself, as it is a Sunni-majority city.
Islamic State militants were preventing people fleeing Mosul, they said, and one said they directed some towards buildings they had recently used themselves. Save The Children operates across several camps in northern Iraq which are still housing people who fled the Mosul after it fell under ISIS control two years ago. US troops can embed at Iraqi army headquarters at the brigade and smaller battalion level, but have so far stayed at the division level.