A meeting of Iraq's Governing Council to finalise the composition of the interim government has been postponed.
There is division over who should get the largely ceremonial job of president
The new body is due to assume power at the end of June. Many posts are already filled, but differences remain over who should be the figurehead president.
Iraqi council members blamed the delay on US officials, who they said were trying to impose their political will.
On Monday a car bomb killed four Iraqis close to the coalition provisional authority headquarters in Baghdad.
Hours earlier, two US marines were killed in clashes with Shia militia in Kufa, just outside the holy city of Najaf.
It was the fourth day of fighting there since radical Shia cleric Moqtada Sadr offered a conditional truce to the US-led coalition forces.
In the southern Iraqi city of Samawa, where Dutch and Japanese peacekeepers are based, a minibus exploded as a US convoy was passing. One bystander was injured.
The BBC's Caroline Hawley in Baghdad says that pushing back the IGC meeting until Tuesday illustrates the deepening disagreement between the US-led coalition and Iraqis over who should be Iraq's president.
Most council members are reported to favour their current head, Ghazi Yawer, a businessman and tribal leader who has been sharply critical of the US-led coalition.
Behind the scenes
But former Foreign Minister Adnan Pachachi is said to be the preferred candidate of the US-led authorities and the United Nations.
Both men are from the Sunni minority.
AFP news agency quoted a senior US official as saying neither candidate was in the running, as the coalition wanted the president and two-thirds of the government to come from outside the council.
He accused council members of "hijacking" the process of forming the government.
Some council members have suggested that US officials may try to break
the deadlock by suggesting a compromise third candidate.
IRAQ SELF-RULE TIMETABLE
30 June: Handover from Coalition Provisional Authority to interim government
End of Jan 2005: Elections to National Assembly
Autumn 2005: New constitution voted on in referendum
December 2005: Full elections for new government
January 2006: Directly elected government takes office
Council members have accused the Americans of trying to cook things behind the scenes.
"There's quite a lot of interference. They should let the Iraqis decide for themselves. This is an Iraqi affair," council member Mahmoud Othman told Reuters.
The council has already chosen former exile Iyad Allawi to become prime minister following the 30 June handover of power.
Correspondents say further haggling is likely over the posts of deputy presidents and key ministers.
But UN officials say things are going as well as they can in the circumstances.
"We will not have a fully representative government... until free and fair elections are held in January of next year," said Ahmed Fawzi, a spokesman for UN special envoy Lakhdar Brahimi.
"Let's not kid ourselves or the Iraqi people. This is going to be an appointed government, and it will be the best we can do under the circumstances, in a traumatised country."