The three Americans -- Paul Slough, Evan Liberty and Dustin Heard -- were sentenced to 15, 14 and 12.5 years respectively in Washington on Thursday, according to a statement released by the United States Attorney's Office for the District of Columbia.

The men, who originally had been sentenced to 30 years each, were members of a Blackwater team named Raven 23 that had been contracted to provide security for US State Department personnel in Iraq.

They opened fire in Baghdad's crowded Nisur Square September 16, 2007 in a bloody episode that caused an international scandal and heightened resentment of the American presence.

"The defendants' orders were for self-defense, and they were firing wildly into cars," Judge Royce Lambert explained in handing down the new sentences, noting that some of the victims were turning around in the other direction.

"There was just wild shooting that could never be condoned by any court," the Justice Department quoted him as saying.

During their lengthy 2014 trial, the Blackwater defendants claimed they acted in self defense in response to insurgent fire.

But no credible evidence was presented that they had indeed come under fire and they were accused of opening fire indiscriminately.

The shooting left at least 14 Iraqi civilians dead and 17 wounded while perpetuating the image of US security contractors run amok.

The three men were convicted of manslaughter, attempted manslaughter and a firearm offense.

A fourth colleague, Nicholas Slatten, was determined to have fired the first shots and was convicted of first-degree murder and sentenced to life in prison.

The sentences were invalidated by an appeals court, which ruled that the men should have been tried separately.

Since then, Slatten was retried and sentenced again in August to life in prison.

Blackwater, founded by Erik Prince, the brother of the current Education Secretary Betsy Devos, was renamed Xe in 2009 and became Academi two years later.