United States military deputy director for operations Brigadier General Mark Kimmitt on Wednesday said his forces detained Amar al-Yasseri, operations director of Shia cleric Moqtada Sadr in Sadr City.
Occupation forces conducted a joint raid with the Iraqi Civil Defence Corps and detained al-Yasseri who is also believed to have been behind the ambush of the US-led troops on 9 October, Kimmitt told a press conference in Baghdad.
Yasseri was captured in the sprawling Shia quarter without incident, he added.
Earlier, the US army ended speculation that Izzat Ibrahim al-Duri, a top lieutenant of Saddam Hussein, was killed or captured in a raid.
But occupation forces managed to net al-Duri's secretary during an operation in northern Iraq on Tuesday morning.
US forces had surrounded areas close to the northern Iraqi city of Kirkuk, giving rise to rumours that they had located al-Duri, the US' second most-wanted man in Iraq after Saddam Hussein.
The Bush administration is eager
to find Izzat Ibrahim al-Duri
"There was a major action against a highly suspicious objective last night in Kirkuk and it is very possible that Izzat Ibrahim has been captured or killed," political analyst Muwaffaq al-Rubai had told reporters, adding he had been in contact with US forces.
Local government officials in Kirkuk, 250km north of Baghdad, said the town was abuzz with talk that al-Duri had been captured.
But US military official told reporters who had accompanied troops on the raid in Hawija: "He was definitely not captured in today's mission".
Al-Duri's aide detained
The police chief of Hawija told AFP, however, al-Duri's secretary had been detained during the sweep of the area.
The US military in October said al-Duri was directly involved in attacks on US troops, and put a $10 million price on his head.
They also claimed to have detained his wife and daughter in the town of Samarra.
Al-Duri is sixth on the US list of most-wanted 55 top Iraqi ex-officials and Baath Party members. But all those in the top five, except for Saddam Hussein, have been killed or captured.