BAGHDAD, Nov 18 (Reuters) - Iraq believes Islamic State militants have stolen more than one million tonnes of grain from the country's north and taken it to two cities they control in neighbouring Syria, the agriculture minister has said.

Falah Hassan al-Zeidan said in a statement posted on the Agriculture Ministry's website on Sunday that the government "had information about the smuggling by Islamic State gangs of more than one million tonnes of wheat and barley from Nineveh Province to the Syrian cities of Raqqa and Deir al-Zor."

Reuters was unable to verify the information.

When Islamic State pushed from Syria into northern Iraq in June, they swiftly took over government grain silos in Nineveh and Salahadeen provinces, where about a third of Iraq's wheat crop and nearly 40 percent of the barley crop is typically grown.

The former head of the Grain Board of Iraq told Reuters in August that Islamic State militants had seized 40,000 to 50,000 tonnes of wheat in Nineveh and the Western province of Anbar and transferred it to Syria for milling.

However, it is not known precisely how much wheat the militants seized over the summer, as they forced hundreds of thousands of people - including many farmers - off their land in what amounted to a purge of the ethnically and religiously diverse area.

The militants' offensive coincided with the harvest of the strategic wheat crop there. Many farmers were unable to sell to the government or to private traders because of the conflict.

Islamic State is hoping to make its self-proclaimed caliphate self-sufficient.

The minister said the militants considered the eastern Syrian cities "safe for them" and thus transferred wheat and barley in Nineveh "to preserve it".

Iraq's grain board imports millions of tonnes of wheat and rice every year. The United Nations Food and Agriculture Organisation predicts Iraq's import needs will grow given "conflict-related challenges to production, storage, and other logistical arrangements", it said in a recent report.

(Writing by Maggie Fick; editing by Susan Thomas)