An Egyptian court has sentenced 78 children to between two and five years in prison for taking part in demonstrations calling for the return of ousted president Mohamed Morsi, judicial sources said.

The authorities have engaged in a crackdown on Morsi’s supporters since his overthrow by the army last year, with hundreds jailed in mass trials which the United Nations has described as “unprecedented in recent history”.

On Wednesday, a court in the Mediterranean city of Alexandria sentenced 78 teenage boys aged from 13 to 17 for joining Muslim Brotherhood rallies during the past three months, a judicial official said.

“The 78 minors, members of the Muslim Brotherhood, were arrested for participating in protests organised by the group calling for the downfall of the regime, where they blocked roads and transportation, and frightened citizens,” state news agency MENA also reported.

Egyptian authorities classified the Muslim Brotherhood as a “terrorist organisation” last December.

Since the army ousted Islamist president Mohamed Morsi in July 2013, the government has launched a bloody crackdown against his supporters, leaving at least 1,400 dead and more than 15,000 jailed.

Several Brotherhood figureheads, including Morsi himself, are facing trials in several cases punishable by death.

About 200 supporters of the Islamist movement have been sentenced to death after speedy mass trials.