Seventy-eight Egyptian minors have been handed sentences of between two and five years in prison by a juvenile court in Alexandria on charges of "belonging to an outlawed group," according to Egypt's state news agency, Al Jazeera reported.
Heavy security was seen outside the court in Alexandria on Wednesday, where judicial sources said those sentenced were aged between 13 and 17.
The minors' lawyers were barred from attending the court hearing while their family members were forced to wait outside.
The 78 minors were arrested for taking part in protests organised by the Muslim Brotherhood that called for the fall of the government and the return of deposed former president Mohamed Morsi to power.
They were also charged for obstructing traffic and for spreading fear among local residents and store owners.
The minors had denied the charges and said that they were arbitrarily arrested. Nevertheless, the presiding judge handed down combined sentences totalling 340 years. Their sentences can be appealed.
Protests against the Egyptian government have been held since the army overthrew Morsi last July following mass protests against his rule.
Demonstrations have been staged in support of Morsi but they have lost strength after a fierce security crackdown against his Muslim Brotherhood party.
At least 1,400 people are estimated to have been killed, more than 15,000 jailed and hundreds sentenced to death since Morsi's outing.
The Muslim Brotherhood has started a social media campaign calling for hunger strikes to take place in solidarity with current Muslim Brotherhood prisoners and in response to what they see as the mistreatment of their members.