While serving in the NATO mission in 2007, the soldiers shelled the Afghan village of Nangar Khel, killing six civilians, including women and children, and injuring two more who later died in hospital.

The military court in Warsaw said there was not sufficient evidence that the soldiers had committed a war crime, bringing to an end the first such trial in Poland, which still has more than 2,500 troops serving in Afghanistan.

"This is an unprecedented event in the history of the Polish judiciary," said the judge, Col. Miroslaw Jaroszewski, adding that the accusation prepared by prosecutors was faulty.

"Lingering doubts cannot be settled to the detriment of the accused," Jaroszewski added. The prosecution has the right of appeal against the verdict.