An audio tape attributed to Osama Bin Laden has called on Iraqis to boycott elections scheduled for 30 January.
The tape's speaker has not been confirmed as Bin Laden
The voice, whose identity cannot be confirmed, says: "Anyone who takes part in these elections will be an infidel."
The recording also backs Jordanian-born militant Abu Musab al-Zarqawi as the al-Qaeda network's leader in Iraq, Arabic TV station al-Jazeera reported.
Iraq's electoral commission criticised al-Jazeera for airing the tape and vowed to push ahead with the poll.
Chief electoral officer Adil al-Lami told the AFP news agency: "We know that Bin Laden is a terrorist, we are going on with our job, we insist on doing the election on time."
He accused al-Jazeera of assisting Bin Laden by passing on his orders to Zarqawi's supporters in Iraq.
A spokesman for al-Jazeera refused to say how or when it received the latest recording.
The network, which broadcast excerpts with a still photograph of Bin Laden wearing a white robe, insists its coverage of Iraq is unbiased.
The tape describes Zarqawi as the "emir" of al-Qaeda in Iraq and praises the "daring operations" of his group against US troops and Iraqi officials.
"The brothers in the group there must listen to him [Zarqawi] and obey him for what is good," the message says.
Zarqawi's al-Qaeda-linked group has claimed responsibility for many bombings and hostage murders in Iraq, including that of UK captive Kenneth Bigley.
The BBC's Heba Saleh, in Cairo, says the chilling message will almost certainly add to the atmosphere of fear surrounding January's election.
He says the speaker has tried to play on the divisions between Iraq's Sunni minority and Shia majority.
Adam Ereli, a spokesman for the US State Department in Washington, said it had not yet been determined whether the voice was that of Bin Laden.
But, speaking to the Associated Press news agency, he described the tape as "a message from terrorists and an attempt by murderers to perpetuate their evil trade".
It was released on the same day that Iraq's main Sunni Muslim political movement, the Iraqi Islamic party, announced it was withdrawing from the elections.
An al-Jazeera presenter said the tape made an indirect plea for help to finance al-Qaeda's activities in Iraq, as well as urging the assassination of those who collaborate with coalition forces.
The speaker also called for supporters to strike Iraqi and Gulf oil pipelines, reiterating a demand made in another audio message attributed to Bin Laden earlier this month.
The militant leader previously made an appearance before the US election on 2 November, in a video tape in which he threatened fresh attacks on the US, whoever was elected.
Bin Laden is widely believed to have been hiding in the mountains along the Pakistan-Afghanistan border since US-backed forces toppled Afghanistan's Taleban regime in late 2001.