Days of rioting after the attack left four people dead

The two were convicted of a grenade attack on a bookshop in 2005 which killed one man and injured another.

The attack set off days of rioting in the predominantly Kurdish south-east.

Observers say the trial is being seen as an important test of whether the judicial system can act independently in cases against the security services.

A court in Van sentenced Ali Kaya and Ozcan Ildeniz to 39 years and five months for the attack on 9 November in the town of Semdinli.

A third man - a former PKK member turned police informer who was arrested with the others - is due to be sentenced in August.

At the time of the attack, the two convicted men were chased and nearly lynched by furious bystanders.

The discovery of weapons and a list of names in their car prompted allegations that they were an undercover execution squad.

The indictment called the attack an act of provocation aimed at stirring unrest among Kurds, discredit the government and undermine Turkey's bid to join the European Union, the AFP news agency said.

The BBC's Meriel Beattie in Ankara says the case has raised questions about the level at which this incident and other alleged abuses might have been sanctioned by the security forces - and about Turkey's ability to make its powerful military accountable for its actions.