MILITARY POWER CURBED
Among other coup generals, retired air force chief Tahsin Sahinkaya is also due to give testimony while navy commander Nejat Tumer died shortly before being called by prosecutors.
The commanders are being investigated on charges of carrying out a coup and trying to change the constitutional order by armed force. A decision on opening a court case will be made after prosecutors complete their investigation.
The military, which has traditionally viewed itself as guardian of the secular state founded by Mustafa Kemal Ataturk in 1923, has carried out three coups between 1960 and 1980.
In 1997 the military pushed an Islamist-led government out of office.
Erdogan's government has reined in the military's power by using reforms undertaken to bring Turkey closer to European Union standards, as the country is bidding for membership.
Turks have also been watching an investigation into an alleged plot to overthrow the government in 2003. On Monday, the secularist Cumhuriyet newspaper reported that 25 officers, including two recently retired heads of the armed forces, could be summoned for questioning.
Some 200 officers, including top generals, have been charged as part of that "Sledgehammer" court case.