He has flown by helicopter into Abu Ghraib prison, the jail at the centre of a scandal over the abuse of detainees by US troops.
The embattled secretary, travelling under tight security to a country where more than 700 US troops have died since last year, earlier landed at Baghdad airport and held meetings with senior US occupation military officers in the capital on Thursday.
Rumsfeld denied on a 15-hour flight from Washington he was trying to cover up the scandal at Abu Ghraib jail near Baghdad.
"If anybody thinks that I'm (in Iraq) to throw water on a fire, they're wrong," he told reporters aboard his aircraft.
"We care about the detainees being treated right. We care about soldiers behaving right. We care about command systems working," added Rumsfeld, who has rejected calls from newspapers and some opposition Democrats to resign.
More courts martial
Earlier the US military said two additional US soldiers will be court martialed on charges of abusing Iraqi prisoners.
Staff Sergeants Ivan "Chip" Frederick and Javal Davis, both reservists, were the second and third of seven US Army military police guards charged with abusing prisoners at the detention facility notorious for its history of torture under ousted President Saddam Hussein.
Frederick, 37, who worked as a civilian prison guard in the US, and Davis, 26, each face five charges.
Both men were charged with conspiracy to maltreat detainees, dereliction of duty for negligently failing to protect detainees from abuse, and maltreatment of detainees and assault.
Frederick was also charged with wrongfully committing an indecent act by watching detainees commit a sexual act. Davis was additionally charged with making false official statements.
Speaking at a Baghdad news conference, US military spokesman Brigadier General Mark Kimmitt said that no dates had been set for the trials of Frederick and Davis. Kimmitt said those trials would be held at Baghdad's heavily guarded convention centre if Sivits' trial goes smoothly there.
Photos of tormented detainees
have caused outrage
In the charge sheet relative to the court martial, US military authorities accused Frederick of placing wires on a prisoner's hands while the latter stood on a box with his head covered.
The prisoner was then told that he would be electrocuted if he fell from the box. The charge sheet alleges that Frederick allowed this episode to be photographed.
The charge sheet also accused Frederick of placing naked prisoners in a human pyramid, jumping on a pile of prisoners, stomping the hands and bare feet of prisoners, forcing male prisoners to perform sex acts, and forcing prisoners to strike one another.
In another charge sheet, US military authorities accused Davis of placing prisoners in a pile on the floor to be assaulted by other soldiers, stomping the hands and feet of prisoners, jumping on piles of prisoners, and lying to investigators about his actions.
The first court martial, of Spec. Jeremy Sivits, will begin next Wednesday, 19 May, Baghdad and be open to the public.