Seif was detained in June 2020 outside the public prosecutor's office as she tried to file a complaint about an assault on her and her mother as they campaigned to communicate with her jailed brother Alaa Abdel Fattah, one of Egypt's best-known activists, rights groups say.

She and her family were among the activists who had campaigned on social media for the release of some prisoners amid fears that coronavirus would spread in prisons.

Three other members of Seif's family were briefly detained in March 2020 for protesting over the same issue.

A Cairo criminal court convicted Seif for spreading and broadcasting false news that would cause panic, the false allegation of the spread of the coronavirus in prisons and misusing social media sites, judicial sources said.

Seif has the right to appeal the ruling within 60 days, they said.

Rights group Amnesty International called the verdict against Seif "yet another crushing blow for the right to freedom of expression in Egypt".

"Egyptian authorities arbitrarily arrested her and have now imprisoned her on bogus charges stemming purely from her peaceful criticism," it said in a statement.

Seif's brother Alaa, a leading activist in the 2011 uprising that toppled former President Hosni Mubarak, was detained in September 2019, six months after his release from a five-year prison term.

Western countries on Friday called on Egypt to end the prosecution of activists, journalists and perceived political opponents under counter-terrorism laws, and to unconditionally release them.

Egypt said it was astonished by the statement, which it called groundless.