Relatives of supporters for ousted Egyptian Islamist president Mohamed Morsi gather outside the courthouse on Tuesday in the central Egyptian city of Minya, during a session of the trial of some 700 Islamists charged with deadly rioting in an Egypt city. Photo: CFP

The leader of Egypt's outlawed Muslim Brotherhood and 682 others went on trial on Tuesday on charges including murder, their lawyer said, a day after more than 500 supporters of deposed Islamist president Mohamed Morsi were sentenced to death.

Brotherhood Supreme Guide Mohamed Badie, 70, and the others were being tried in the same court in Minya Province that condemned 529 members of the Islamist group to death, in what rights groups said was the biggest mass death sentence handed out in Egypt's modern history.

The UN human rights office said on Tuesday the mass death sentences contravened international law, and voiced concern for others facing the same charges. The European Union and the United States also criticized the ruling.

The army has cracked down hard on the Brotherhood since it toppled Morsi, Egypt's first freely elected president, in July.

In August, security forces killed hundreds of Brotherhood supporters who staged a long sit-in to demand Morsi's reinstatement. Thousands of others were arrested and top leaders, including Morsi himself, are also on trial.

Defense lawyers boycotted Tuesday's court session - attended by 60 of the defendants - after complaining of irregularities.

"We refrained from attending ... because the judge has violated criminal law procedures and did not allow the [lawyers] to present their defense," Adel Ali, a member of the defense team, told Reuters.

He said that 77 of the defendants were in custody while the rest had either been released on bail or were on the run.

A government spokesman declined to comment, saying the case is too sensitive.

The mass trials will ratchet up tensions and could trigger more violence in the biggest Arab state, which has been dogged by political upheaval since a popular uprising backed by the army toppled veteran leader Hosni Mubarak's fall in 2011.

An Islamist alliance which includes the Brotherhood has urged Egyptians to take to the streets in politically sensitive areas of Cairo to protest against the mass trials, despite severe restrictions having been imposed on demonstrations.

The sites include the Rabaa al-Adawiya mosque, scene of one of two pro-Morsi protest camps and Tahrir Square, the symbolic heart of the revolt against Mubarak.

Islamist militants in Sinai near Israel's border have stepped up attacks against police and soldiers since Morsi was deposed and Field Marshal Abdel Fattah al-Sisi installed an army-backed government.

Hundreds have been killed and the insurgency is spreading across the country, with shootings, suicide bombings and assassinations of senior Interior Ministry officials.

Reuters