Turkey's landmark trial into the bloody 1980 coup resumed on Friday in the absence of the two defendants, whose old age and frail health is still preventing them from appearing in court.

The two generals, Kenan Evren, 94, and Tahsin Sahinkaya, 86, are considered unfit to appear in the dock because of their age and physical condition, according to a report by the Institute of Forensic Medicine in Istanbul.

Evren and Sahinkaya are being treated in military hospitals for medical complications arising from chronic diseases, which the report said "could be life threatening" under stress.

It is the first time that the perpetrators of one of the country's several military coups have faced justice, and lawyers for the plaintiffs are keen for the defendants to appear in the dock.

The trial opened in Ankara in April, but Evren, the junta leader who was declared president after the coup, and Sahinkaya, then air force commander, have been absent from the hearings pending the medical assessments.

Lawyers for the civil plaintiffs in the case -- victims of the coup -- have asked judges to reject the report and are seeking an independent commission to examine the condition of the two generals.

The once-untouchable Turkish army has overthrown civilian governments three times since 1960, and drove an Islamist government out of office in a bloodless coup in 1997.

Fifty people were executed, 600,000 arrested, dozens died of torture and many others went missing after the 1980 coup.

The trial is seen as part of a power struggle between the army and the government of the Islamist-rooted Justice and Development Party, which has drastically reduced the military's influence in politics in the last decade.

About 300 people staged a demonstration outside the palace of justice in the Turkish capital on Friday calling for the judicial authorities to punish the accused and ensure that the trial is not merely symbolic.

The two generals could face life imprisonment if found guilty of crimes against the state.