EGYPT'S chief prosecutor has ordered two new mass trials for 919 suspected Islamists on charges that include murder, despite international criticism of an earlier trial that issued death sentences against hundreds of defendants.

Students, most of them Islamists, held protests against the death sentences in several universities, turning into clashes with security forces that left one 18-year-old student dead at Cairo University.

The new trials will be held in Minya province, south of Cairo, where a judge on Monday sentenced 529 defendants to death on charges of killing a police officer during an attack on a police station last summer.

The verdict brought an outcry from rights groups and criticism from the UN, EU and US over the cursory trial, which lasted only two sessions and in which lawyers said they were denied the right to make their case or question witnesses.

Egyptian authorities are holding a series of mass trials in a crackdown on the Muslim Brotherhood and other supporters of Mohamed Morsi since the military removed him in July last year. Some 16,000 have been arrested over the past months, including most of the Brotherhood's top leaders.

The new trials bring the total number of defendants in Minya along to 2147 in four trials, including the one in which the verdicts were issued on Monday.

All the trials are connected to a wave of violence in mid-August 2013 after security forces broke up two pro-Morsi sit-ins in Cairo.

More than 600 were killed in the sit-in break-up, setting off a backlash of violence which lasted several days.