The supreme leader of the Muslim Brotherhood has been sentenced to death with 682 other people after a five-minute hearing which will renew international concern over Egypt's so-called "road-map to democracy".

Mohammed Badie was found guilty of inciting riots in the town of Edwa last summer which led to mass arrests of what the authorities said were Brotherhood supporters furious at the overthrow of President Mohammed Morsi.

No attempt was made at least in the public hearing to distinguish the parts played by any of the other hundreds of defendants in the riots, in which churches, businesses and government offices were burned down and some policemen killed.

In the same hearing, the judge, Said Yussef, commuted to life imprisonment all but 37 of the 529 death penalties he handed down in a separate case last month, linked to a similar riot in the nearby town of Mattay. He gave no explanation for the decision, though the verdicts had been automatically referred to Egypt's Grand Mufti for a clerical opinion.

Life terms in Egypt usually mean 25 years in jail.

Relatives of many of those on trial claimed that they were not even present during the riots, and said they were being victimised for petty local feuds.

When news of the sentences came through, relatives of those accused broke into howls of anguish and fell to the ground. The streets outside the court, in the provincial capital Minya, were blocked off by police and soldiers with armoured personnel carriers.

Neither the accused nor their families were allowed in court, and no-one came out to read the lists of names of those whose death penalties had been confirmed in the Mattay case.

"I do not know whether my husband's case has been commuted or not," said Mona Shahada, whose husband Mohammed Ali Ahmed was sentenced to death last month along with his brother, son-in-law and another relative. Their 13-year-old son, Mahmoud, stood in tears next to her.

"But then it makes no difference. It's a disaster, a catastrophe - our home is destroyed and who will raise this child?"

She said her husband, a technical studies teacher, had been at school all morning on August 14, when the mob swept through.

The riots were triggered by the police and army's decision to break up protest sit-ins in Cairo with force. About 1,000 Brotherhood supporters were gunned down.

That day remains a fraught dividing line in Egyptian society, with many backers of the army and its head, Field Marshal Abdulfattah el-Sisi, enthusiastically backing the death sentences and calling for more Muslim Brotherhood supporters to be killed.

The Brotherhood, most of whose leadership is now in prison, has called Field Marshall Sisi a mass murderer and demanded he be referred to the International Criminal Court.

The severity of the sentences in the Minya cases and the lack of due process - in both cases, no evidence was presented in court for either the prosecution or defence, and verdicts were handed down at the start of only the second session - have also shocked Egypt's international backers.

Amnesty International called them "grotesque".

"Our right to present our defence was not recognised," said Mohammed Abdulwahhab, a defence lawyer in the Edwa case. "This does not happen in a state where the rule of law is followed. We are opposed to criminality but this was not justice."

Despite the headline figures, few expect the cases to end in actual executions. The cases will now go to the appeal court, which until now at least has a higher reputation for independence.

In the Edwa case, only 77 of the 683 are currently in custody. If any of the others are brought before a court, a retrial is automatic in the case of the death penalty.

Badie is facing a string of other serious cases in Cairo, some alongside Morsi, any of which could also end in the death penalty. The decision of whether actually to kill the head of the world's most prominent Islamist organisation will be the key test of the new regime, particularly if as expected Field Marshal Sisi is elected president next month.

He will have ultimate authority to issue a pardon, and will be aware of the precedent set by Gamal Abdul Nasser, the colonel who led the coup that overthrew the monarchy in the Fifties. He executed the then most prominent Brotherhood leader, Sayyed Qutb, making him a martyr for subsequent generations.

Since then, the Brotherhood has formally renounced violence, but is still accused by the authorities of being a "terrorist organisation".

The Brotherhood has widespread support in Upper Egypt. But many of those arrested in the current cases seem to come from outside its base in the provincial middle classes.