US forces raided a northern Iraqi town near Kirkuk overnight, possibly in search of a top Saddam Hussein deputy.
The US says Ibrahim is behind some attacks on its troops
The target seems to have been Izzat Ibrahim al-Douri, the highest ranking regime official still at large other than Saddam Hussein himself.
A member of Iraq's governing council told the BBC he had been captured, but there has been no confirmation.
The BBC's Nick Childs at the Pentagon says officials there could not verify the story, but did not deny it either.
He says one official said he was "sceptical" about the report.
The US military has not commented on the raid, which an Iraqi official called the largest ever in the region.
The US has a $10m bounty on Mr Douri, who it accuses of being one of the key organisers of the insurgency around Samarra and Tikrit.
Saddam Hussein biographer Simon Henderson told the BBC that the capture of Mr Douri would be "a considerable victory for the Americans and a considerable defeat for the insurgency".
The French news agency AFP said Mr Douri's eldest son Ahmad has been commanding two insurgent brigades of 250 men each.
Ahmad is receiving instructions and funds from his father, AFP reported, citing an Iraqi police official.
The unnamed official said several members of the brigades had been captured in the overnight raids in the town of Hawijah, 45km (30miles) west of Kirkuk.
One of Mr Douri's wives and a daughter were detained last week, along with the son of his doctor.
The raid comes amid an ongoing dispute about a battle in Samarra on Sunday.
The US says as many as 54 people were killed when two American convoys came under attack in the city, but morgue officials say they handled only eight dead.
US Brigadier General Mark Kimmett has said the military's figures are only estimates, based on what he called battlefield reports.
No Americans were killed in the battle, the fiercest since George Bush declared major combat operations at an end on 1 May.
NOVEMBER DEATHS IN IRAQ
US troops: 79
Non-US forces: 26
Foreign civilians: 6
Iraqis killed by insurgents: At least 32*
Iraqis killed by coalition troops: At least 64*
*No official statistics are kept for Iraqi deaths
The convoys that came under attack were carrying new Iraqi banknotes.
The battle rounded off a month that saw the highest number of US casualties in the country since the war.
A US soldier was killed by a roadside bomb on Tuesday as a convoy left Samarra, military sources said.
Close to Saddam
Mr Douri, the possible target of Monday night's raid, was one of Saddam Hussein's closest and most trusted associates.
Mr Henderson, the Saddam Hussein biographer, said Mr Douri is likely to have been in touch with the deposed Iraqi leader - and might know where he is.
But he said it is not clear that Mr Douri would voluntarily tell the Americans that information even if captured alive.
He is rumoured to be in poor health, and is known to have suffered from leukaemia in the past.
Mr Douri was one of the key plotters who carried out the coup that brought the Baath Party to power in 1968.
In later years he served as the Iraqi leader's number two in the powerful Revolution Command Council, as vice-chairman.
He is the King of Clubs in the US "most wanted" deck of cards issued to help identify former regime members.