Croatian Foreign Ministry spokeswoman Ivana Crnic did not say if Croatia plans to respond to the request.
Lawyers are seeking Aziz's release on medical grounds. His lawyer, Badee Izzat Aref, believes the 69-year-old Aziz "is in his last days."
Aziz was arrested after the 2003 U.S.-led invasion of Iraq that toppled the Iraqi regime led by Saddam Hussein. With the agreement of Iraq's new government, he is currently being held in a U.S. detention facility.
Saddam Hussein In Pictures
A slideshow of photographs from Saddam Hussein's years ruling Iraq through his downfall.