A US Marine accused over the killing of 24 Iraqi civilians in 2005 was demoted to the rank of private on Tuesday but will serve no time behind bars, a military spokesman said.

Staff Sergeant Frank Wuterich, who led an eight-man squad whose other members have all been let off, was sentenced to 90 days confinement but he will not serve them due to a pre-trial deal, the spokesman told the media

The 31-year-old admitted one count of negligent dereliction of duty on Monday, but charges of manslaughter over the killings – whose victims included women and children -- were dropped as part of a plea deal.

"Wuterich is sentenced to 90 days of confinement and reduction to private (E-1)," said a statement from Camp Pendleton, California, where Wuterich has been on court martial for the last three weeks.

But it said: "Per the terms of the pre-trial agreement, the convening authority disapproved any adjudged confinement and therefore Staff Sergeant Wuterich will not serve any of the confinement sentence."

The judge said he wasn't reducing Wuterich's pay because of his financial situation being a single father.

‘Not a baby killer’

In all, 24 Iraqi civilians were killed – 19 in several houses along with five men who pulled up in a car where the marines were on patrol in the Iraqi town of Haditha on November 19, 2005.

The victims included 10 women or children killed at point-blank range. Six people were killed in one house, most shot in the head, including women and children huddled in a bedroom.

Before he was sentenced Wuterich voiced sorrow on Tuesday, but insisted he was not a ‘cold-blooded baby killer’.

Addressing three surviving family members of those killed in Haditha, he said: "Words cannot express my sorrow for the loss of your loved ones. I know there is nothing I can say to ease your pain.

"I wish to assure you that on that day, it was never my intention to harm you or your families. I know that you are the real victims of November 19, 2005," he said, reading from a prepared statement.

But he added: "For six years, I have had to accept that my name will always be associated with a massacre, being a cold-blooded baby killer, an 'out of control' monster, and a conspiring liar.

"There's nothing I can do about whoever believes these things. All I can do is continue to be who I've always been – me. And none of those labels have ever been, or ever will be, who I am."

‘Was doing my duty’

In his statement, made in a resonant, calm voice after witness testimony, Wuterich insisted he was only doing his duty.

"Many of the Marines who were there that day, along with everyone who has stood by me and supported me, may be disappointed that I pled guilty. It might suggest that I believe we behaved badly or dishonorably.

"The truth is, I don't believe anyone in my squad... behaved in any way that was dishonorable or contrary to the highest ideals that we all live by as Marines.

"But even with the best intentions, sometimes combat actions can cause tragic results," he said, adding that he had "never fired my weapon at any women or children that day."

The other seven Marines charged in the case have been exonerated through various legal rulings, fueling anger in Iraq, where authorities had pushed for US troops to be subject to Iraqi justice before the US pullout in December.