"My testimony is invalid. I signed it without knowing the content," Firat Altin, a former Kurdish militant, told the court in Diyarbakir, adding that he had faced "threats and blackmail" by judicial officials.

Another witness, Hidir Altug, said he testified under pressure from a former police chief and was made to memorise the allegations he made.

The indictment says Colonel Cemal Temizoz set up a rogue unit that detained and questioned people for helping Kurdish rebels when he served in southeastern Sirnak province from 1993-1996.

Acting on orders from Temizoz, the unit allegedly killed some of those questioned, often burying the bodies in remote areas.

The six other defendants include former militants of the Kurdistan Workers' Party (PKK) who became informers and collaborated with the military and members of the so-called "village guard" -- a local Kurdish militia armed by the government to help the army against the PKK.

All seven suspects risk life sentences withouth the possibility of parole.

The case has been hailed as a major step in shedding light on widespread allegations that the security forces acted outside the law in their struggle against the PKK in the 1990s when the group's armed campaign reached its peak.

In the first hearing last week, Temizoz rejected the charges, saying the murders were committed by PKK rebels themselves as part of in-fighting within the group, or as part of personal setting of accounts and blood feuds, which are frequent in the Kurdish-majority southeast.

The indictment followed excavations in the region in March and April that resulted in the discovery of bone fragments.

The probe began after a former PKK member who later became an informer said several people who disappeared in the 1990s were executed summarily.

The PKK, listed as a terrorist group by Ankara and much of the international community, took up arms in 1984, sparking a conflict that has claimed some 45,000 lives.