Saddam Hussein has dismissed evidence suggesting he approved the execution of people under 18 - the minimum age for death sentences under his rule.
Saddam Hussein's trial resumed after a three-week break
He was being cross-examined for the first time about the killing of Shias in the town of Dujail, following an attempt to assassinate him in 1982.
He also said prosecution witnesses at his trial in Baghdad had been bribed and coached in what to say.
A defence lawyer was ejected from court after an altercation with the judge.
She was ordered from the hearing when she tried to display photos of Iraqis tortured in US-run prisons.
"This is what the Americans did to Iraqis in Abu Ghraib," she said, as the court was examining alleged deaths during interrogation under Saddam Hussein's rule.
The judge later told her she would not be penalised for her outburst, and she could resume her place in court.
Saddam Hussein, who appeared on his own, is on trial with seven others for the killing of 148 people in 1982.
During Wednesday's proceedings, the prosecution produced documents suggesting that 28 people whose executions Saddam approved had been under 18.
Chief prosecutor Jaafar al-Moussawi presented the court with some of the identification cards of the children and read out their dates of birth.
But Saddam said ID cards could easily be forged.
He told the court: "There is a clear ulterior motive by those who have given you these documents," the Associated Press news agency reported.
"You can buy IDs like this in the market. Is it the responsibility of the head of the state to check the IDs of defendants and see how old he is?"
The day began with acrimonious exchanges between the trial judge and the ousted Iraqi leader himself.
When told by the judge to refrain from political statements, Saddam Hussein said: "You're scared of the interior minister, he doesn't scare my dog."
The interior ministry has been accused of human rights violations under the new regime.
Saddam's latest trial appearance comes a day after the court announced that he would face new charges of genocide and crimes against humanity.
The charges relate to a military campaign against Kurds in northern Iraq in the late 1980s, in which as many as 180,000 people may have died.
The new charges, which came at the end of a three-week break in the trial, refer to a campaign known as the Anfal. The case will be tried separately.
The former leader demanded that an international body examine signatures on an order approving death sentences against those accused of organising an assassination attempt against him in Dujail in 1982.
He has previously acknowledged ordering the trial in which many people were sentenced to death, but has said his actions were legal.
Some of Saddam's co-defendants, who have already testified, said their signatures were forged.
In further testimony, he said witnesses presented by the prosecution in the case were bribed.
"The witnesses who testified were brought here after being bribed and briefed of what was to be said," he said, the AFP news agency reported.
He also challenged the judge, saying: "Who could dare to give a verdict against the president who defended his country and stood up against those who fought with Iraq?"
Previous trial sessions have been halted by protests from the defendants. All of the accused deny the charges.
The trial was adjourned until Thursday.