Turkey's Court of Appeals on Thursday overturned an Istanbul criminal court's ruling that witnessed 275 defendants sentenced in 2013 for involvement in an alleged criminal network conspiring to overthrow the ruling Freedom and Justice Party (AKP).

"There is no incidence of admission of 'Ergenekon terror organization' by the local court, it remains unclear who formed it [the alleged terror group], when [it was formed], failure of revealing its crimes and hierarchical structures, and its leader is also unknown," the court said in its ruling, according to state-run Anadolu Agency.

Ilker Basbug, a former general chief of staff who presided over Turkey's armed forces, was the top-ranking official to be convicted in the 2013 ruling.

The appeals court also found Basbug's objection to his trial at the Supreme Criminal Tribunal was justified.

The defendants in the court case were linked to an attack on a state building, which resulted in the death of a judge and four others being wounded. State prosecutors also linked the "Ergenekon" terrorist network to a cache of explosives discovered at the residence of an ex-military officer.

Coup-less

Turkey's armed forces - seen as guardians of the modern secular state - staged coups in 1960, 1971 and 1980, along with a soft coup in 1997.

However, the military has distanced itself from such interventions, making its latest political statement on the subject last month. In March, Turky's armed forces threatened legal action against unnamed media outlets for allegedly spreading rumors that they were planning a coup to oust President Recep Tayyip Erdogan.