The US ambassador to Iraq, Ryan Crocker, has told the Washington Post newspaper that he intends to leave his post early next year, to retire.
Crocker has said troops should leave Iraq only if conditions allow
Reports have said Mr Crocker may leave Baghdad as soon as mid-January, before a new American president takes office.
Mr Crocker has repeatedly said that US troop withdrawals from Iraq should depend on conditions on the ground and not on timetables set in Washington.
This puts him at odds with the policies of some presidential candidates.
"I am prepared to remain in Baghdad until early 2009, when I intend to retire," Mr Crocker told the Washington Post.
"That will make two years in Iraq and 37 years in the Foreign Service - it's enough!"
Mr Crocker arrived in Baghdad in March 2007.
He is a fluent Arabic speaker who has worked as a diplomat in Pakistan, Syria, Lebanon and Kuwait.
Mr Crocker is credited with bringing in a number of experienced diplomats into the US embassy in Baghdad and restoring a sense of discipline to America's largest diplomatic mission, the Washington Post said.
Gen David Petraeus is also expected to leave Iraq on a scheduled rotation of duties just before Mr Crocker has said he will retire.
Gen Petraeus is credited with successfully implementing the US troop surge that is partly behind the reduction of violence in Iraq.