The Iraqi politician managing interim leader Iyad Allawi's election campaign has resigned from the government in protest at the conduct of US troops.
US troops are regularly accused of insensitivity towards Iraqis
Minister of State Adnan Janabi stepped down after US troops apparently held him in handcuffs for more than 30 minutes at a Baghdad roadblock.
He is expected to continue in his role preparing Mr Allawi's party for elections due on 30 January.
Iraq's interim leaders often accuse US troops of insensitivity.
According to the BBC's Jim Muir in Baghdad, Mr Janabi's resignation is being seen largely as a protest at the Americans' perceived arrogance in their dealings with the interim Iraqi government.
Mr Allawi is trying to persuade Mr Janabi to retract his resignation, the prime minister's office said.
Mr Janabi was reportedly detained on Wednesday at a checkpoint bordering the Green Zone, the heavily-fortified compound that serves as a Baghdad base for US officials and their Iraqi appointees.
As campaign manager for the party headed by Mr Allawi, Mr Janabi earlier this week had to fend off accusations of bribing journalists.
Following revelations that reporters at a campaign meeting received gifts of $100 bills, he told London's Daily Telegraph newspaper the gesture was "just hospitality".
"If we wanted to bribe the press, we would have to pay a lot more," he said.