The occupation troops’ deputy director of operations, Brigadier General Mark Kimmitt, had described the captive Sayed Amir Yassari as "operations director in Sadr City of Muqtada Sadr".
But in the face of strong denials from a Sadr spokesman that Yassari had any current position in his organisation, another US spokesman on Thursday backtracked on the accusations against the cleric, who has substantial support.
The report of a link between Yassari and Sadr was "speculation" based on "gossip from the street", said Captain Sean Kirley, spokesman for the 2nd Armoured Cavalry Regiment, which patrols the area.
Earlier, aides of Muqtada Sadr, who runs the anti-US Mahdi Army militia, denied any connection with the US detainee, suspected of being behind attacks on US soldiers and Iraqi civilians in the capital.
Sadr's Mahdi Army has had a stormy relationship with the US military.
The US has been unable to control
Meanwhile, resistance fighters attacked a police station in western Iraq and a mine blew up a US military vehicle in Baghdad on Thursday.
Three civilians and two policemen were wounded in the attack on the police station in the heart of the western town of Ramadi.
Attackers fired small arms and rocket-propelled grenades from a black BMW in the assault in Ramadi.
"One police major, Muhammad Ibrahim, was wounded in the leg and one policeman called Muhannad Sallun is seriously hurt and has been transferred to Baghdad," deputy police chief Lieutenant Samir Habib Jalil said.
"Four grenades were thrown and shots fired from automatic weapons against the station and police riposted," said witness Luai Abdul Karim.
In the capital, smoke was seen pouring out of a field artillery ammunition support vehicle after it hit a landmine at a major motorway intersection.
"The vehicle did catch fire but there were no injuries," a US spokesman said.
In Brussels, US Secretary of State Colin Powell called on NATO to take on a greater role in Iraq, saying the country's stability is critical for everyone.
Powell asks NATO to shoulder
Powell said on Thursday that the 19-member Alliance had already provided logistical support to the Polish division of a multi-national force in Iraq, according to prepared remarks to NATO foreign ministers meeting in the Belgian capital.
Sixteen NATO members are part of the coalition in the occupied country.
Powell also recalled that UN Security Council resolution 1511 passed on 16 October "encourages the engagement of multilateral and regional organisations in this effort."
The toll among occupation troops is rising as more Iraqis take up resistance against foreign forces.
NATO chief, George Robertson, echoed Powell's call in his opening address at the two-day meeting.
"The Alliance must continue to help NATO countries who take on leadership roles in Iraq, and prepare itself to take on new roles and missions where necessary," he said.