ANKARA, Turkey (AP) -- Turkey's prime minister on Tuesday urged one of Iraq's two vice presidents to delay a referendum on the future of Kirkuk, fearing Iraqi Kurdish groups could seize control of the northern, oil-rich city.

Turkey, which has been trying to quell a Kurdish insurgency for more than two decades, is concerned about the growing power of Iraqi Kurds and has repeatedly warned Iraqi Kurdish groups against trying to seize control of Kirkuk.

Iraq's constitution calls for a referendum on Kirkuk's future by the end of the year. The Kurds want to incorporate the city and its rich oilfields into their self-ruled region _ a move the Turks have strongly opposed.

Turkey's Prime Minister Recep Tayyip Erdogan told Iraqi Vice President Adil Abdul-Mahdi the normalization of security sought by the Iraqi constitution has not occurred in Kirkuk and the referendum must be postponed, the state-run Anatolia news agency reported.

Turkey fears Iraq's Kurds want Kirkuk's oil revenues to fund a bid for independence that could encourage separatist Kurdish guerrillas in Turkey, who have been fighting for autonomy since 1984. The conflict has claimed the lives of 37,000 people.

Erdogan also asked Abdul-Mahdi to stop attacks by separatist Kurdish guerrillas, based in Iraq, on Turkey.

Kirkuk, an ancient city that once was part of the Ottoman Empire, has a large minority of ethnic Turks as well as Christians, Shiite and Sunni Arabs, Armenians and Assyrians. The city is just south of the autonomous Kurdish region stretching across three provinces of northeastern Iraq.

Since the U.S.-led invasion of Iraq in 2003, thousands of Kurds pushed out of the region under Saddam Hussein's rule have returned.

Turkey _ a predominantly Muslim country that is an ally of the U.S. and NATO, a friend of Israel and a candidate to join the European Union _ is pushing to increase its influence in the Middle East, where it says it can help negotiate between Islamic countries and the West.

Turkey has not ruled out military incursions into Iraq to hunt separatist Kurds, despite warnings from Washington, which fears that such a move could lead to tensions with the Iraqi Kurdish groups who have been important allies of the U.S.

By Selcan Hacaoglu