Tony Blair has condemned as "completely and totally unacceptable" pictures which appear to show the torture of an Iraqi prisoner by British soldiers.
The paper claims British soldiers handed over the photos
If the pictures, published in the Daily Mirror, prove to be genuine Mr Blair said he would "condemn it utterly".
"We went to Iraq to get rid of that sort of thing, not to do it," he added.
But the PM said, if there had been any abuse it was "exceptional", and should not detract from the good work being done by UK armed forces in Iraq.
There were thousands of British troops doing a "brave and extraordinary job" to make life better for the Iraqi people.
Earlier Armed Forces Minister Adam Ingram agreed the pictures were "appalling" if they were genuine.
They "besmirch the good name of the armed forces," he said.
Military police are conducting an investigation into the photos which appear to show a soldier using violence and urinating on a captive.
Mr Ingram said this investigation had to be given time.
Pictures showing American troops humiliating Iraqi prisoners, with a hooded and naked prisoner standing on a box with wires attached to his genitals, also generated outrage earlier this week.
US President George W Bush vowed that those responsible would be "taken care of".
Mr Ingram said there was no "culture of abuse" in the British Army despite the fact that five separate inquiries into maltreatment are under way.
He admitted: "If these allegations are true, they are appalling, they are despicable and there can be no justification for them at all."
And he said the inquiry by the Royal Military Police's Special Investigations Branch would "not leave any stone unturned".
Those who are opposed to the coalition's occupation of Iraq would employ "full exploitation of these incidents", Mr Ingram said.
The Mirror says the pictures were handed over by British soldiers from the Queen's Lancashire Regiment who claimed a rogue element in the British army was responsible for abusing prisoners and civilians.
Speaking on condition of anonymity, the soldiers told the paper no charges were brought against the unnamed captive.
They allege that during his eight-hour ordeal he was threatened with execution, his jaw broken and his teeth smashed.
After being beaten and urinated on, he was driven away and
dumped from the back of a moving vehicle, the soldiers claimed, unaware if he was dead.
The images have already been seen in the Middle East
The reason for making the photos public was, they said, to show why the US-UK
coalition was encountering such fierce resistance in Iraq.
One told the paper: "We are not helping ourselves out there. We are never
going to get them on our side. We are fighting a losing war."
Army spokesman Roger Goodwin, on behalf of the Queen's Lancashire Regiment, said there was "clearly some form of link to the regiment".
"But the precise form of that link, including whether the soldiers involved in the alleged atrocities were members of the QLR, needs to be established.
He added: "There is no place in our regiment for individuals capable of such appalling and sickening behaviour.
"The sooner they are exposed and ejected from the regiment, the better."
The regimental secretary, retired Lt Col John Downham, said: "We are furious that these people, whoever they turn out to be, have already besmirched our hard-earned good name and let down the many hundreds of QLR soldiers whose outstandingly successful tour in Basra was recognised by no fewer than 21 honours and awards."
In a press conference, Sir Mike Jackson, Chief of General Staff, said: "If proven, the perpetrators are not fit to wear the Queen's uniform and they have besmirched the Army's good name and conduct."
The British have previously enjoyed a relatively positive image
Ahmed al-Sheik, editor-in-chief of Arab TV news channel, said the photographs would outrage Arabs around the world.
"These scenes are humiliating not only to the Iraqis, but to every Arab
citizen around the world," he told BBC Two's Newsnight.
Meanwhile former foreign secretary Lord Hurd said the situation in Iraq was in danger of spiralling out of control.
"In Iraq we're in a nosedive. Things are happening which were entirely predictable and predicted.
"An army of liberation, particularly a British/American one, turns within hours into an army of occupation."