The supreme court has refused to consider appeals by the former Blackwater security contractors convicted in the 2007 slaying of 14 Iraqi civilians at a crowded traffic junction in Baghdad that marked one of the lowest points in the bloody conflict.

The court announced on Monday that it will not hear an appeal brought by the four men convicted in 2014 trial. They worked for the North Carolina-based private security firm then called Blackwater Worldwide that was contracted by the US government to provide security to US officials working in Iraq.

One of the men, Nicholas Slatten, is going to be retried, beginning 11 June, after an appeals court in Washington DC ruled last summer that he should have been tried separately from his three co-defendants.

Slatten was convicted of first-degree murder after the court heard he was the first to open fire.

The team was providing security to a US diplomat in an armed convoy in September 2007 during one of the most fierce phases of the war, near Nisour Square in Baghdad, where insurgent attacks and car bombs were common threats. Without warning, the men opened fire on the crowds, using machine guns and grenade launchers to mow down Iraqi motorists and unarmed civilians, including children. The barrage killed 14 and wounded at least 17. It triggered international outrage over the role of security contractors working for the US government in a war zone and a row over whether the men should be tried in Iraq or America.

Three of the men, Paul Slough, Evan Liberty and Dustin Heard, were convicted in 2014 of manslaughter and other charges at trial in Washington and sentenced to 30 years in prison apiece. Nicholas Slatten was convicted of murder and given a life sentence.

In August 2017 an appeals court threw out Slatten’s conviction and ordered his retrial. He is expected to argue that he did not fire first. The other men were ordered to be resentenced because 30 years was deemed too long, and a date has yet to be set. Blackwater has been sold and renamed.