The US military says it is questioning four people, including one who they say is a bodyguard and long-time associate of ousted Iraqi President Saddam Hussein.
The suspected guard was wrestled to the ground
The man has been named as Adnan Abdullah Abid al-Musslit - said by locals to have been brought back from retirement just before the war.
He was captured along with the others in a pre-dawn raid in Saddam Hussein's hometown, Tikrit - the last city to fall to coalition forces.
According to the Associated Press, the other men detained included the former head of security in Tikrit, Daher Ziana, and a militia leader, Rafa Idham Ibrahim al-Hassan.
Since Saddam Hussein's feared sons Uday and Qusay were killed last week, US military officials say more and more Iraqis are coming forward with tip-offs.
The US has offered $25m for information leading to the capture of Saddam Hussein, or proof of his death.
Army spokesman Jeff Fitzgibbons told the BBC that the US troops had been able to close in on the suspects without any forewarning, thus avoiding any shoot-out.
Dozens of soldiers were involved in the raids on two or three homes in an upmarket area of Tikrit.
The raids were the latest in a series of attempts to trap the deposed leader and his entourage.
US Deputy Secretary of State Richard Armitage said on Monday that troops carrying out such raids in Iraq "were just hours behind Saddam Hussein".
Mr Armitage told CNN that although the US was keen to capture the ousted leader alive, if such an action posed a risk to US troops they would kill him without hesitation.
In a comment on the continuing bloodshed in Iraq, the US armed forces chief, General Richard Myers, has said central Iraq continues to be a "war zone".
Speaking during a visit to India, he said 80% of security incidents were taking place in the area between Baghdad and Tikrit.
The man believed to be a bodyguard of Saddam Hussein did try to resist arrest, said Lieutenant Steve Russell, but he was wrestled to the ground and dragged down the stairs.
The suspect was led away bleeding, attended by a medic who treated him after he was placed in the back of a Humvee armoured vehicle.
Adnan Abdullah Abid al-Musslit is pictured with Saddam Hussein
"We got our prime target. This man was a close associate of Saddam Hussein," Lieutenant Russell said.
"Every guy we get tightens the noose."
US troops have staged a number of raids in recent days, stepping up their search for the ousted Iraqi leader.
But the BBC's Caroline Hawley in Iraq says not all of the information the Americans have been receiving has been accurate.
On Sunday, soldiers from Task Force 20, the secretive special team set up to hunt for the ex-leader and his inner circle, staged an assault on a house in Baghdad.
They did not capture anyone, but during the raid they opened fire on two cars passing nearby, killing five Iraqi civilians.
The Tikrit raid came after another day of casualties for the US forces, as one soldier was killed and three wounded in a grenade attack in central Baghdad.
It took to 50 the number of US troops killed in hostile attacks in Iraq since the US declared major hostilities over on 1 May.