The acquittal came after the prosecution argued that the defendants acted in self-defence in the November 2004 shooting of Ahmet Kaymaz and his 12-year-old son, Ugur, outside their house in Kiziltepe, in Mardin province.

The indictment originally called for up to six years in prison for the four officers on the grounds that their action went beyond the limits of self-defence.

Lawyers for the victim's relatives said they would appeal the sentence.

Police said Kaymaz and his son were gunned down in an operation against rebels from the outlawed Kurdistan Workers' Party (PKK), but local activists and neighbours said the two were unarmed civilians.

A parliamentary investigation in 2004 accused police of "heavy negligence" and concluded that Kaymaz and his son could have been captured unharmed.

The incident had created a furore in Turkey and the trial was moved from Mardin to the western city of Eskisehir for security reasons.

Turkish security forces have faced widespread accusations of human rights abuses in their fight against the PKK, which took up arms for self-rule in the southeast in 1984 and is listed as a terrorist group by Ankara and much of the international community.

But the authorities have been reluctant to look into such cases and convictions of security personnel for torture or other abuses have been rare.

Cases of rights abuses are seen as a test for Turkey's commitment to respect democratic norms in its bid to join the European Union.