The closure was a key step towards fulfilling a US-Iraqi agreement signed last year which mandates the handover of security responsibilities to sole Iraqi control.
The so-called Status of Forces Agreement (Sofa) which also calls for all US troops to withdraw from Iraq by 2012, obliges the United States to set free detainees who do not face Iraqi arrest warrants or detention orders.
About 8,300 detainees remain in US custody in Iraq, either in Camp Cropper near Baghdad airport or at Camp Taji, which lies north of the Iraqi capital.
US military commanders say they expect all Iraqi detainees to be handed over to Iraqi authorities by January, although the security pact does not set a deadline.
Camp Taji is scheduled to transfered to Iraqi control on January 10, but Brigadier General David Quantock, the commander of US detention operations, said that he may hold back the handover.
"If I have to shift this transition to the right because they [the Iraqi authorities] are not ready we'll shift it to the right ... If they are not ready [for Taji] they're not getting it," he said.
Bucca was opened after the Abu Ghraib scandal in 2004, when pictures emerged of US soldiers at the west Baghdad jail abusing and sexually humiliating detainees.
The US policy of holding suspects without trial has fuelled anger among Iraqi towards the US military.
|Iraqi detainees faced severe abuse at the Abu Ghraib jail when it was under US control [AFP]
Quantock said that while many innocent people were probably rounded-up in by the US military in the early days of the war, he said that those who are still in custody were "not an accident".
About 100,000 people have been detained by US forces since the 2003 invasion.
Speaking on the terms of the bilateral security pact, the US vice-president said on Thursday that Washington will respect Iraq's wishes if the country's government decides to speed up the timetable for the withdrawal of US troops from the country.
"Whatever the Iraqi people decide, we will abide by it," Joe Biden said in Baghdad on Thursday.
But Biden said that Iraq has to take several steps before it can call a referendum to alter the security agreement.
The agreement currently mandates the withdrawal of US combat forces by the end of August 2010 and all US troops by the end of the following year.
Baghdad has agreed to hold the referendum along with parliamentary elections in January. If voters reject the pact in the referendum, US forces will have a year to withdraw instead of by the end of 2011.