European Union foreign policy chief Catherine Ashton has voiced alarm at the death sentences handed out to more than 500 supporters of deposed president Mohamed Morsi.
"The EU opposes capital punishment under all circumstances. The death penalty is cruel and inhuman, fails to act as a deterrent and represents an unacceptable denial of human dignity and integrity," Ashton said in a statement issued hours after the verdict on Monday.
The senior diplomat urged Egypt to ensure "the defendants' rights to a fair and timely trial," saying this is particularly important for the credibility of Egypt's transition towards democracy.
On Monday, a court in southern Egyptian sentenced 529 supporters of Morsi's Muslim Brotherhood movement to death on charges that included the killing of a policeman, the attempted murder of two others and the storming of a police station in Minya governorate.
The allegations are related to violence the broke out in the aftermath of the forced dispersal of two pro-Morsi protest camps in Cairo on 14 August.
Monday's verdict, the biggest mass death sentence in Egypt's modern history, has sparked local and international outrage.
Washington questioned the fairness of the proceedings as the trial took just two days.
"It defies logic that over 529 defendants could be tried in a two-day period in accordance with international standards," deputy US State Department spokeswoman Marie Harf told a regular press briefing.
Washington was "deeply concerned" and "shocked" by the sentences, she said.
Harf said the US still viewed its ties with Egypt as important. "We don't want to completely cut off the relationship"
The US has suspended much of its $1.5 billion in military and economic aid to Egypt last year pending progress towards democracy.