The United States said it is "shocked" and "deeply concerned" by the death sentences handed down to 529 members of Egypt's outlawed Muslim Brotherhood.
U.S. State Department spokeswoman Marie Harf said Monday it seems impossible that hundreds of defendants could be tried in accordance with international standards in only two days.
An Egyptian court sentenced the members of the Islamist group to death on charges that include the murder of a police officer, attacking a police station and other acts of violence.
The court in Minya, about 200 kilometers south of Cairo, rendered the verdict just two days after the trial began Saturday. Those convicted can appeal the decision.
More than 100 of the defendants were in custody, but most were tried in absentia. The court acquitted 16 people.
The charges are related to clashes in Minya last August. That violence erupted after security forces in Cairo broke up two Brotherhood protest camps, leaving hundreds of people dead.
They were protesting the army's ouster of president Mohamed Morsi, a Brotherhood member who has been in custody since he was removed from office in July and is facing several trials himself.
Egypt's interim authorities have cracked down on the Brotherhood, labeling it a terrorist group and arresting many of its leaders.