"Aziz called me and said he was being held in the Kadhimiya prison in Baghdad."
Aref also warned that his client's life was in danger, saying that Iraqi authorities might execute him. Several other high-ranking Baathists, including Saddam and Ali Hassan al-Majid, known as Chemical Ali, have been executed by the Iraqi government in recent years.
Aziz surrendered himself shortly after the US invasion of Iraq in 2003. He was brought to trial five years later, and in 2009, he was sentenced to 22 years in prison for two separate crimes.
He received a 15-year sentence for the summary executions of dozens of people in 1992, and a seven-year sentence for helping to displace thousands of Kurds from nothern Iraq.
The 74-year-old Aziz was one of the most recognisable faces of Saddam Hussein's administration. A longtime member of the Baath Party, he served terms as both Iraq's foreign minister and deputy prime minister.
Aziz took part in the Geneva peace conference in 1991, which aimed to head off the first Gulf War by finding a diplomatic solution to Iraq's occupation of Kuwait. And in the days before the second US invasion of Iraq, in 2003, Aziz held a high-profile meeting with the late Pope John Paul II.
Camp Cropper handover
The handover was announced one day before Iraqi authorities take control of Camp Cropper, the last US-run detention facility in Iraq. Ibrahim said several more detainees would be turned over in the next 24 hours.
But the US military says it will keep control of roughly 200 prisoners even after the handover.
US authorities will continue to oversee some operations at the prison until the end of the year.