Nechirvan Barzani, prime minister of the autonomus Kurdish government, told AFP that his government favoured postponing the vote.

"The regional government is in favour of this extension," said Barzani who was in Najaf to meet influential Shiite cleric Grand Ayatollah Ali al-Sistani.

According to article 140 of the Iraqi constitution the referendum had been due to be held by the end of 2007 but has been delayed "for technical reasons," he said.

Barzani added that the six-month extension should be used for a UN-supervised mechanism to sort out the issue of Kirkuk, which sits on the second-largest oil and gas reserves in Iraq.

The city has been gripped by ethnic tension since the 2003 US-led invasion, with Kurds demanding its incorporation into the autonomous Kurdish region, while Arab and ethnic Turkmen oppose this, fearing they would be marginalised.

Kirkuk is claimed by both the Arabs and the Kurds.