The CNN-Turk and NTV news channels said police arrested Ibrahim Firtina, former air force chief; Ozden Ornek, a former navy chief; and at least five other retired senior officials.

Those held were taken to Istanbul for questioning by anti-terror police.

'Psychological campaign'

Firtina and Ornek were linked to a purported 2003 plot to discredit the AKP government, a plan revealed by the liberal Taraf daily in January.

The plan, codenamed Sledgehammer, involved bombing two Istanbul mosques and escalating tensions with Greece by forcing Greek jets to down a Turkish plane over the Aegean Sea.

The act would have been an attempt to show the Turkish government as inept, according to documents obtained by Taraf.

The Turkish army said the documents were discussed in a seminar on war-time contingency plans, but denied they represented a coup plot.

The allegations have caused Basbug to complain of a "psychological campaign" to smear the army and warn of a possible "confrontation between institutions".

Academics in the net

Prosecutors so far have charged more than 400 people in the case, including soldiers as well as academics, journalists and politicians.

Turkey's secular military has ousted four governments since 1960, proof to many that it has been the real power in the country since Mustafa Kemal Ataturk set up the republic from the ashes of the Ottoman Empire.

Under EU pressure, however, Erdogan has dramatically curtailed the military's power and reinforced its place under civilian rule, while also bolstering democratic institutions.

On Sunday, the prime minister announced new plans to overhaul the judiciary and the Constitution, a legacy of the 1980 military coup.