The United States and its allies must think carefully before launching an offensive to retake the Iraqi city of Mosul from Islamic State, Turkey's defence minister said on Tuesday, saying it could trigger an exodus of one million more refugees.

Earlier on Tuesday, Turkish Prime Minister Binali Yildirim described plans for the expected assault on Iraq's second largest city as "not transparent", underscoring what appears to be growing concern from a NATO ally about the operation.
Defence Minister Fikri Isik said any refugee flows out of Mosul, a city of more than two million people that has been in the hands of Islamic State since 2014, needed to be contained within Iraq's borders.
"Our allies should weigh up very carefully the migration wave of about one million set to be caused by a possible Mosul operation," he said in a statement.
"The migration should be absorbed in Iraq's territory. Otherwise it will impose a large burden on Turkey and that will affect Europe."
Turkey is already home to more than 2.5 million refugees from the conflict in Syria, where Turkish forces are now engaged in an expanding operation in the north, backing rebel groups in their fight against Islamic State.
Turkey is also using the operation to push back the Kurdish YPG militia, which it regards as a terrorist group and does not want encroaching on its territory. The YPG are supported by the United States.
Speaking in the Turkish parliament, Yildirim said the YPG were now filling a vacuum left by the expulsion of Islamic State from the area, and said Turkish forces were prepared to "cleanse" the YPG.
"Terrorist organisations need to leave the area... We, as Turkey, are determined," he said. "We know how to cleanse the PYD/YPG, just as we cleansed Daesh from Jarablus," he said, referring to Islamic State's presence in the Syrian town.
Yildirim also said that an assault on Mosul might lead to another round of sectarian conflict, saying the demographic make-up of both Syria and Iraq was being dangerously shaken up.
"The Mosul plans of our allies are unfortunately not transparent, they include the risk of sectarian clashes.
"The disturbance of the demographic structure in Syria and Iraq and the alteration of ethnic areas will not bring stability to the region. Handing over Mosul, where Sunni tribes are effective, to Shi'ite militants would be lighting a fire."
It is not clear when any US-coordinated offensive on Mosul might begin, but expectations have been building.
At the same time there has been a push by US-supported groups on the Islamic State stronghold of Raqqa in Syria, and on Dabiq, a village in northwestern Syria that is symbolically important to the group.