Turkish President Tayyip Erdogan on Tuesday called on Iraqi Kurds to lower the Kurdish flag in the northern Iraqi city of Kirkuk, warning that failure to do so would damage their relations with Turkey. Kirkuk, one of Iraq's disputed territories, has Kurdish, Arab, and Turkmen populations. Kurdish peshmerga forces took control of it in 2014 when Islamic State overran around a third of Iraq and the army's northern divisions disintegrated. "We don't agree with the claim 'Kirkuk is for the Kurds' at all. Kirkuk is for the Turkmen, Arabs and Kurds, if they are there. Do not enter into a claim it's yours or the price will be heavy. You will harm dialogue with Turkey," Erdogan said. "Bring that flag down immediately," he said at a rally in the Black Sea province of Zonguldak, where he was campaigning ahead of an April 16 referendum on constitutional changes that would broaden his powers. Kurds have long claimed Kirkuk and its huge oil reserves. They regard the city, just outside their semi-autonomous Kurdistan region in northern Iraq, as their historical capital. The local Rudaw TV channel cited the governor of Kirkuk as saying that the Kurdistan flag should fly alongside the Iraqi national flag because the city is largely under the protection of Kurdish forces. Turkey has long seen itself as the protector of Iraq's Turkmen ethnic minority. Local media reported that leaders of Kirkuk's Turkmen communities have rejected the raising of the Kurdish flag as against the constitution. Turkey fears territorial gains by some Kurdish groups in Iraq and neighboring Syria could fuel Kurdish separatist ambitions inside Turkey, where PKK militants have fought an insurgency against the state for more than three decades.