Bahrain strips 36 Shia nationals of citizenship

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", the judicial source told AFP.

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 1 May, Amnesty said.

"[The timeing] 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.

Meanwhile, reports have emerged that the health of jailed Bahraini activist Nabeel Rajab has worsened.

"Nabeel Rajab is suffering from health problems that have developed or deteriorated during more than 10 months of arbitrary detention," Human Rights Watch said on Wednesday.