Straw did not give any time frame for the withdrawal and said specifically that it would only begin "as and when the Iraqis are satisfied that their own forces can cope completely with the responsibility."
Straw said that the withdrawal would start in one or two provinces outside the southern city of Al-Basrah and its launch would only be a matter of months.
Straw arrived in Iraq on 6 January.
Meetings With Senior Iraqi Officials
He has met with Iraqi Prime Minister Ibrahim al-Ja'fari and President Jalal Talabani.
"My main message has been one of support for the stated policy of the political leaders to form this government of national unity, broadly based," Straw said at a joint news conference today with President Talabani.
"I'm glad to tell you that in principle we [Iraqi political leaders] are agreed to have a national unity government," Talabani added. "Everyone is expecting to have it as soon as possible, but you know the devil is in the details. For that, we hope that we will be able to solve it as soon as possible. I'm expecting some weeks."