The authorities led by President Abdel Fattah al-Sisi, a former army chief who ousted his predecessor Mohamed Morsi in July 2013, have cracked down on Islamist and secular opponents with hundreds dead and thousands in jail.
The Carter Center, which opened an Egypt office in 2011 after the Arab Spring uprising, said it would not send an observation mission to assess parliamentary elections expected there later this year.
"Both Egyptian civil society and international organisations face an increasingly restrictive environment that hinders their ability to conduct credible election observation," the group said in a statement on Wednesday.
"The current environment in Egypt is not conducive to genuine democratic and civic participation," former president Carter said in the statement.
The group traditionally deploys observers in elections across the world.
Its statement denounced "the crackdown on dissidents, opposition groups, and critical journalists, together with heightened restrictions on core freedoms of expression, assembly and association".
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It voiced concern about the mass arrests of Muslim Brotherhood supporters and the introduction of a protest law late last year.
More than 15,000 supporters of Morsi and his Muslim Brotherhood have been arrested in the crackdown.
Dozens of secular activists have been jailed for breaking the protest law, which bans rallies except those sanctioned by police.
"Taken together the restrictions on democratic freedoms mean that citizens and political parties face extreme limitations on debate and participation and that political campaigning could be extremely difficult – and possibly dangerous – for critics of the regime," the Carter Center said.
At least 1,400 people have been killed in the crackdown targeting Morsi supporters, while hundreds have been sentenced to death.
Morsi and the top leaders of the Brotherhood are also on trial.