US Vice-President Joe Biden is in Baghdad for talks with Iraqi political leaders to try to resolve a dispute threatening parliamentary elections due to be held in March.
More than 500 candidates, including several prominent Sunni Arabs, have been disqualified on suspicion of loyalty to Saddam Hussein's outlawed Baath Party.
The BBC reports the dispute has caused bitter recriminations among Iraqi politicians.
Mr Biden began by meeting the UN secretary general's special representative for Iraq before holding talks with Prime Minister Nouri Maliki. He was also to meet President Jalal Talabani and other key political figures.
Mr Biden says the election on 7 March must be fair, credible and transparent, but he insists Washington will not interfere in the dispute.