The last US Marine charged over a notorious incident in which civilians were gunned down in Iraq pleaded not guilty Thursday, as his military trial got under way in California.

Staff Sergeant Frank Wuterich, 31, faces nine counts of voluntary manslaughter and other charges for his role in 24 deaths, many of them women and children, in the Iraqi town of Haditha on November 19, 2005.

Proceedings started with jury selection, which was delayed by two hours and then dragged on for much of the day at the Camp Pendleton military base in southern California where Wuterich will be tried over the next month.

Wuterich formally entered "not guilty" pleas to all charges, including counts of dereliction of duty and assault. If convicted of all the offenses, Wuterich could be sentenced to more than 150 years in prison.

But his lead lawyer said he was confident the Iraq veteran would be exonerated.

"We're confident that the truth about Haditha will come out during the trial and that Staff Sergeant Wuterich will be acquitted of all charges," Neal Puckett told AFP ahead of the start of jury selection.

Wuterich, who had no previous combat experience, was the squad leader who sent his men into a village to hunt for insurgents following a roadside bombing that killed a fellow Marine and injured two other US troopers.

Nineteen people were killed inside houses, along with five men who pulled up near the scene in a car, triggering one of the most controversial criminal cases involving the US military during the nearly nine-year-long Iraq war.

The Marines said after the violence in Haditha that 15 Iraqis had been killed by the roadside bomb that killed the American soldier.

But a subsequent investigation by Time magazine showed most of the dead were killed as Marines swept through three houses near the site of the bombing.

Lawyers for the Marines said insurgents hid behind civilian homes and opened fire, sparking a shootout that would fall within legal rules of engagement.

But military prosecutors said there were no such insurgents and that the Marines initiated a bloody three-hour rampage to avenge the death of their comrade.

Among the victims, 10 were women or children, killed at point-blank range.

The other seven Marines charged in the case have been exonerated through various legal rulings.

But Wuterich's attorneys have exhausted all possible appeals on behalf of their client, including an attempt to dismiss charges based on the forced retirement of one of the military defense attorneys.

Another ruling against the defense team allowed military prosecutors access to unaired portions of the CBS "60 Minutes" interview of Wuterich, which was conducted prior to charges being filed.

Wuterich remains on active duty at Camp Pendleton while awaiting resolution of his case.

He could be sentenced to life in prison, but military juries in Iraq-related Camp Pendleton trials have been reluctant to convict their peers or have recommended very light sentences.

Wuterich has asked for his jury to include enlisted personnel, and recent trials have included many Iraq and Afghanistan veterans. At least one third of the jury -- comprising at least five members -- must be enlisted personnel.

Opening statements could be heard later Thursday, if time allows, although by mid-afternoon jury selection was continuing, with the judge interviewing individual jury candidates after they had been questioned by lawyers.