President Jalal Talabani of Iraq telephoned Turkey's Prime Minister Recep Tayyip Erdogan late on Monday to express "regret over the latest statements by Massud Barzani," Erdogan's spokesman, Mehmet Akif Beki, told AFP.

Beki added that "Talabani underlined that they place great importance to ties with Turkey".

Barzani, head of the autonomous Kurdish region in northern Iraq, was quoted over the weekend as threatening to interfere in Turkey's restive southeast if Ankara continued to oppose Kurdish claims on the oil-rich Iraq city of Kirkuk.

Responding to the remarks, Erdogan warned Iraqi Kurds on Monday that hostility toward his country could result in a "very heavy cost" for them in the future and charged that the Iraqi Kurdish leader had "overstepped the line".

Turkey says the referendum on Kirkuk's future status, scheduled for the end of the year, should be postponed arguing that thousands of Kurds have been moved into the city to change its demography.

Ankara worries that Kurdish control of Kirkuk and its vast oil reserves would embolden what it believes are Kurdish ambitions to break away from Baghdad.

Kurdish independence in Iraq, it fears, could fuel the two-decade separatist insurgency led by the separatist Kurdistan Workers' Party (PKK) in southeast Turkey, which has already resulted in more than 37,000 deaths.

Tensions are already high between the two sides over Turkish accusations that Iraqi Kurds tolerate, and even support, thousands of PKK rebels who have found refuge in the mountains of northern Iraq.

Beki said Erdogan urged Talabani during their telephone conversation to take measures against militants of the separatist Kurdistan Workers' Party (PKK) holed up in northern Iraq.

"Talabani said they were ready to fight against the PKK as part of a common plan with Ankara," the spokesman added.

Turkey has long pressed Baghdad and the United States to crack down on PKK camps in northern Iraq where, it claims the rebels are able to obtain weapons and explosives for attacks on Turkish targets.

The US says it is working to curb the PKK through non-military means such as cutting off its financial resources.

Ankara has threatened a cross-border operation into northern Iraq to crack down on the rebel camps if Baghdad and Washington fail to act against them.