A Bahraini court sentenced 57 men to 15-year jail terms on Monday for rioting in a prison outside the capital Manama last March, the public prosecutor's office said.
Bahraini security forces tear-gassed and beat inmates at Jaw prison on Mar. 8 while trying to quell clashes that erupted during family visits, local human rights group Bahrain Youth Society for Human rights said at the time.
Bahrain's public prosecutor said in a statement that the convicts had "unleashed acts of chaos, riots and rebellion inside (prison) buildings".
Jaw prison is the main facility for hundreds of people jailed over participation in anti-government protests, political violence, or involvement in armed attacks on security forces or civilians.
Bahrain, a small island state linked to Saudi Arabia by a 25 km (15 mile) causeway, is strategically important to the West as it hosts the U.S. Fifth Fleet.
Tensions have flared in the kingdom since the 2011 "Arab Spring" uprisings led to protests in which Bahrain's Shi'ite majority demanded more rights from the Sunni monarchy. Saudi Arabia's Sunni Muslim rulers also accuse Iran's Shi'ite leadership of trying to stir unrest.
Charges in the prison riot included damaging public property, attacking police, arson and resisting authorities.
Pictures posted on social media of the prison had shown a person with a bandaged head and a man with a bleeding arm. Other photos showed young men standing in a room with overturned furniture or strewn with plastic bags.
It was not possible to verify the authenticity of the photographs, or where they were taken.
Mohammed al-Tajer, the lawyer, lamented the outcome and said that alleged violence against the inmates was ignored.
"We raised a complaint that our clients were beaten during the unrest in Jaw prison, but the court sentenced them at the end of the day, ignoring these complaints.
(Reporting By Gulf Bureau; editing by Dominic Evans)