A court in Bahrain on Tuesday jailed 36 Shias convicted of forming a "terrorist" group to attack police, and stripped them of their citizenship, a judicial source said.
Three of those sentenced received life terms, while the rest were jailed for between three and 10 years, the source said.
The defendants had been charged with "forming an illegal group that aimed to jeopardise the constitution and laws... using terrorism as one of its means," according to the judicial source.
They were also accused of "possessing explosives without permits", the source said, adding that the defendants confessed to taking part in riots and vandalism.
The Sunni-ruled kingdom has been the scene of frequent protests and clashes with police since security forces quelled Shia-led nationwide protests in 2011 that called for political reforms.
Hundreds of Bahrainis have been arrested and several high-profile figures, including Shia clerics, stripped of citizenship.
Amnesty International on Tuesday accused authorities of "dramatically" escalating the crackdown on perceived critics, with 32 people summoned by the public prosecution within five days.
The rights group said that at least 24 have since been charged with "illegally gathering".
"The intensified crackdown against Bahraini dissidents in recent days is highly alarming and exposes the shocking extremes to which Bahrain's authorities are prepared to go to silence criticism of their human rights record," said Samah Hadid, head of campaigns at Amnesty's Beirut office.
The measures come ahead of Bahrain's UN human rights review session in Geneva on May 1, Amnesty said, adding that the timing "strongly suggests that this is part of a deliberate attempt to prevent peaceful critics from speaking out about the government's record in Geneva".
Amnesty said those summoned included lawyers, rights and political activists and relatives of "victims of human rights violations".
Eight of those charged were told they are banned from travelling, and four have so far been prevented from leaving the country, Amnesty said.