"Because of the population that has been shifted to Kirkuk, the referendum foreseen under constitutional provisions for the end of 2007 will create controversy and render the problem even more difficult," Sezer said.

"We believe the status of Kirkuk should be determined not by a forced referendum but through a formula which all Iraqi groups will agree to without the pressure of a deadline," he said.

Sezer was speaking at an economic cooperation meeting here of countries from the Organization of the Islamic Conference (OIC).

Ankara accuses Iraqi Kurds of having moved thousands of their people to Kirkuk and its environs since the US-led invasion of Iraq in 2003 in a bid to change its demographic structure in their favor ahead of the referendum.

Iraqi Kurdish leaders want to incorporate the city and its rich oil fields into their autonomous region in the north -- a move seen here as a part of Kurdish designs to break away from Baghdad.

An independent Kurdish state, Ankara fears, would fuel separatism among its own restive Kurds in neighboring southeast Turkey, sparking regional turmoil.

Kirkuk also has sizeable Arab and Turkmen communities, the latter of Turkish descent and backed by Ankara, who oppose the city's shift to the Kurdish region.

Kirkuk has been hit in recent months by a series of deadly explosions blamed on Sunni Arab extremists who oppose Kurdish claims on the city, as well as Iraq's embattled US-backed government.