More than 2,000 Iraqis in the northern province of Nineveh have been executed by Islamic State militants controlling the area, the defense minister said on Friday.

Ministry officials could not confirm when or how the deaths had occurred, and Reuters was unable to immediately confirm the government's claims.

Access is severely restricted in large parts of Iraq's north and west, which Islamic State militants have controlled since sweeping across the Syrian border in mid-2014 in a bid to establish a modern caliphate.