The man in charge of security for US diplomats in Iraq has resigned after heavy criticism of how foreign private security firms in Iraq are supervised.
Richard Griffin was appointed in June 2005
US state department official Richard Griffin did not mention the issue in his resignation letter.
But he left just a day after the department moved to strengthen government oversight of the firms.
The changes were prompted by the deaths of Iraqi civilians in an incident involving the Blackwater company.
At present, foreign private security contractors have immunity from prosecution under Iraqi law but the Iraqi government is reportedly preparing a bill to make them accountable locally.
Iraqi government spokesman Ali al-Dabbagh told Reuters news agency that the bill was being discussed in the cabinet and would be submitted to parliament "soon".
Mr Griffin supervised the diplomatic security bureau at the state department in Washington.
The US anti-war movement has been mocking security contractors
On Tuesday his boss, US Secretary of State Condoleezza Rice, accepted the terms of an internal report which identified an urgent need for tougher oversight of the private firms which currently protect State Department and some other US employees in Iraq.
The biggest and best-known of the companies is Blackwater.
The Iraqi government accuses Blackwater of killing 17 innocent civilians in Baghdad last month and says it wants the firm out of the country.
The head of Blackwater denies the killings were unprovoked, insisting his men had been fired upon.
Since the incident five weeks ago the extensive use in Iraq of private security has become highly controversial in America, the BBC's Vincent Dowd reports from Washington.
This week's state department report said there have been serious lapses in how the firms are supervised.
It is clear it was September's incident in particular, and the questions it raised in Iraq and the US, which led to Mr Griffin's sudden departure after 36 years in government service, our correspondent says.
For its part, the state department will hope a change at the top will start to restore confidence in the way America carries out and supervises diplomatic protection in Iraq, he adds.