The prime minister has apologised for any cases of mistreatment of Iraqi prisoners by British soldiers in an interview on French television.
Mr Blair said anyone responsible for abuse would be punished
Tony Blair promised those responsible would be punished under military rules.
Defence Secretary Geoff Hoon is to field MPs' questions about the alleged abuse in the Commons on Monday.
He will face pressure to reveal when the claims first surfaced after Downing Street confirmed it had a Red Cross report in February raising concerns.
Human rights group Amnesty says it warned last May that Iraqis had been tortured and killed in UK custody.
Mr Blair, speaking on French television during a trip to France to mark Europe Day, said: "We apologise deeply to anyone who has been mistreated by any of our soldiers. That is absolutely and totally unacceptable.
"Those who are responsible for this - if they have behaved in this appalling way - they will be punished according to the Army disciplinary rules.
"I hope people understand, though, that is not what the majority of our soldiers are doing there.
"The activities of a few people who have brought shame to their situation should not detract from the work done by the vast majority."
The Ministry of Defence (MoD) said it was "not likely" the confidential Red Cross document would be published, saying action had already been taken.
Shadow foreign secretary Michael Ancram called on the government to come to the Commons and "come clean" about the situation, what it knew and when, and its response to the Red Cross report.
"If we are to have confidence in what is happening in Iraq it's very important that the government does come clean," he said.
"It is terribly important that the morale of our troops and the confidence of people in those troops is sustained."
He said Mr Hoon also had questions to answer on the preparations for the 30 June handover.
Liberal Democrat leader Charles Kennedy has called on the government to publish whatever evidence it may have been given by the Red Cross.
The Daily Mirror published photos allegedly showing prisoner abuse
The Defence Secretary's statement will come less than a week after Armed Forces Minister Adam Ingram made a Commons statement on abuse allegations.
He pledged the government would "leave no stone unturned" in their investigation and said inquiries had already been made into 33 cases of civilian deaths, injuries or ill treatment in Iraq.
A MoD spokeswoman confirmed the government had been "investigating certain cases for several months".
She was unable to confirm whether the cases were linked to the Red Cross report or claims by Amnesty International, or when the government had first been alerted to allegations of abuse.
But Amnesty International said it had already voiced UK abuse concerns to government officials in a series of meetings held over the past year.
"Instead of an impartial and civilian-led inquiry to get to the truth, we continue to see secretive investigations by the Royal Military Police," an Amnesty spokesman said.