The United States is ramping up pressure on Egypt to reverse the death sentences given to 529 supporters of ousted president Mohamed Morsi.
US Secretary of State John Kerry, during a surprise trip to Jordan on Wednesday, criticised the legal process that led to the sentences, saying it "simply defies logic".
"I am deeply, deeply troubled by the sudden and unprecedented decision by an Egyptian court to issue preliminary death sentences for 529 citizens after a quick mass trial," Mr Kerry said in a statement.
"It is impossible to believe that such a proceeding satisfied even the most basic standards of justice," he said.
The roughly 1200 defendants in the case, including the 529 sentenced on Monday, are accused of murder and attempted murder in connection with the deaths of two Egyptian policemen during riots in Minya, south of Cairo, on August 14.
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The rioting erupted as news spread that police had killed hundreds of supporters of Morsi, who was toppled by the army in July, while dispersing two Cairo protest camps.
Mr Kerry said the start of a second trial meant there was "greater urgency" to ensure due process.
Egypt's Muslim Brotherhood leader Mohamed Badie went on trial in Cairo on Tuesday along with hundreds of other Islamists before the same judge who passed the death sentences on Monday.
"I urge the interim Egyptian government to reverse the court ruling and ensure due process for the accused. Anything less would dishonour the bravery of all who sacrificed their lives for democratic values," Mr Kerry said.
