Four Polish soldiers, accused of committing war crimes in Afghanistan, on Wednesday faced the first day of a re-trial after Poland's Supreme Court last year overturned their acquittal, a military court spokesman said.
The case marks the first instance in which Polish troops have faced a court martial for war crimes while fighting abroad.
The men are suspected in connection with the August 2007 deaths of six civilians in the Afghan village of Nangar Khel, in the mountainous southeastern province of Paktika.
The victims included a man, two women and three children who were killed by machinegun fire and shrapnel.
All members of Poland's contingent in NATO's International Security Assistance Force (ISAF), the soldiers opened fire with mortars and automatic weapons on the village claiming they had been responding to an attack by Taliban rebels.
In a previous ruling, in June 2011, a Polish court cleared them for lack of evidence they had intended to attack civilians.
But in March 2012, the Supreme court overturned the acquittal, arguing that evidence suggesting the deaths were "a deliberate act" had been overlooked.
Prosecutors have said the deaths occurred several hours after the Poles had responded to another attack on a separate patrol.
Three of the four accused face life in prison if found guilty.
The fourth, who is not accused of deliberately killing civilians but only of opening fire on a civilian target, faces 15 years imprisonment.
All of them have pleaded not guilty, claiming that the civilian deaths resulted from faulty mortar equipment when they responded to a Taliban attack.
Ex-communist Poland, which joined NATO in 1999, has some 1,800 troops deployed in Afghanistan with NATO's ISAF mission fighting a Taliban insurgency.
Close to 40 Polish military personnel have died there since the mission began in 2002.