Iraqi Prime Minister Nouri al-Maliki has told the US that while he is a friend, he is not America's man in Iraq, according to a senior aide.
Mr Maliki has disagreed with the US over a timeline for reform
Mr Maliki made his comments in a meeting on Friday with the US envoy in Baghdad, Zalmay Khalilzad.
The talks were meant to smooth tensions between the two sides over the US plan to introduce a timetable for reforms aimed at ending sectarian violence.
On Saturday Mr Maliki was to hold video talks with US President George W Bush.
On Friday, Mr Maliki and Mr Khalilzad issued a rare joint statement emphasising the need to work together to end the bloodshed.
They pledged a "good and strong" relationship and said the government had "timelines to take positive steps forward".
But during the meeting, Mr Maliki is reported to have spoken firmly to the US representative.
"I am elected by a people and a parliament. Security should be co-ordinated with me. Decisions should not be unilateral," senior aide Hassan al-Suneid quoted him as saying.
"I am a friend of the United States, but I am not America's man in Iraq."
On Tuesday Mr Khalilzad outlined initiatives to try to stabilise Iraq, including a plan to reform Iraqi security ministries.
The US wants Iraqi security forces to take charge of security duties
He said the Iraqi government had agreed to develop a timeline for progress by the end of the year.
At a joint news conference, the top US military commander in Iraq, Gen George Casey, said Iraqi security forces could be able to assume responsibility for the whole country within 18 months.
But divisions emerged between the two sides over the next two days.
"I affirm that this government represents the will of the people and no one has the right to impose a timetable on it," Mr Maliki said at a news conference on Wednesday.
The stipulation of a timeline was, he said, the product of US domestic politics.
"I am positive that this is not the official policy of the American government but rather a result of the ongoing election campaign," he said then.
US involvement in Iraq and the ongoing violence there have become key issues ahead of US mid-term elections, which take place next month.