Al-Azzawi is the fourth regime member to be captured
The captured former Iraqi finance minister could reveal key information about secret funds believed to have been held abroad by the ousted regime, coalition forces say.
Iraqi police arrested Hikmat Ibrahim al-Azzawi in Baghdad and handed him over to US marines on Saturday.
He is number 45 on the coalition's list of 55 most wanted supporters of Saddam Hussein and the eight of diamonds in the US forces' pack of cards featuring fugitive Iraqi officials.
A Central Command spokesman, Captain Stewart Upton, said Mr al-Azzawi "could have information on the locations of money that belongs to the Iraqi people".
CAPTURED IRAQI LEADERS (AS RANKED BY US FORCES)
24. Samir al-Aziz al-Najem
45. Hikmat Ibrahim al-Azzawi
51. Watban Ibrahim al-Tikriti
52. Barzan Ibrahim al-Tikriti
55. General Amir al-Saadi (surrendered)
Iraq is desperately in need of such funds following the massive damage caused to its infrastructure during the war.
Saddam Hussein is thought to have amassed up to $24bn during his 24-year rule - and much of it may be hidden in offshore accounts.
The ousted president's half-brother Barzan al-Tikriti, once Iraq's ambassador to the UN in Geneva and alleged "banker in the West," is also in custody.
US marines involved in seizing control of Baghdad have now withdrawn from the city, handing over to regular US troops.
The BBC's Richard Galpin says the army will be focusing on the critical issues facing the population - getting the city's water and electricity up and running and establishing law and order.
Iraq's neighbours want US forces to pull out as soon as possible
A few street lights came on for the first time in 10 days in central Baghdad - an indication that some generators have been repaired.
But, in a further sign of chaos, looters can now be seen selling stolen weapons and ammunition - including Kalashnikov assault rifles - openly on the streets, he says.
Mounds of rotting rubbish are piling up across the city and some people are still having to draw water from the River Tigris, which is polluted with raw sewage.
The United Nations says its first big food convoy to be sent to Baghdad, which had been due to arrive on Friday, has still to reach the city.
MIDDLE EAST AFTER SADDAM
The after-effects of the war for the region
Less than half of Baghdad's hospitals are functioning - the rest have been ransacked by looters, Roland Huguenin-Benjamin of the
International Committee of the Red Cross (ICRC) told the BBC.
The lack of electricity means that medicines cannot be refrigerated and hospital equipment does not work, he said.
The BBC's Caroline Hawley in Baghdad says Iraqis remain deeply suspicious of American motives, noting that the oil ministry is one of the few government buildings not to have been looted.
Mass demonstrations against the US presence are a daily occurrence, she says.
Foreign ministers of the six states which border Iraq, plus Egypt and Bahrain, have called for US-led forces to pull out of Iraq as soon as possible.
They also demanded the speedy formation of a representative government, with a central role for the United Nations.
In other developments:
US officials say an Iraqi once involved in the suspected nerve gas programme - Imad Hussein Abdallah al-Ani - has surrendered to US forces
US officials say an "international terrorist" belonging to the Palestinian Abu Nidal organisation, Khala Khadr al-Salahat, has surrendered to US marines
A slow train leaves the southern port of Umm Qasr heading for Iraq's second city Basra - the first rail journey in post-Saddam Hussein Iraq
A power struggle grips the eastern Iraqi city of Kut, where the town hall has been taken over by an Iranian-backed Shia Muslim leader accompanied by thousands of local supporters
In an Easter radio address, President George Bush expresses sympathy for relatives of US servicemen killed in Iraq
- An international team of zoologists and vets is delayed in Kuwait on its way to assess conditions at Baghdad zoo, where many animals are without food.