A Bahraini court on Thursday sentenced prominent Shiite rights activist Nabeel Rajab to three years in prison over \"unauthorised\" protests against the Gulf state\'s Sunni Al-Khalifa monarchy, a lawyer said. \"The court has sentenced Nabeel Rajab to three years in jail over three cases of taking part in unauthorised protests,\" lawyer Mohammed al-Jishi wrote on his Twitter page. Jishi said the defence team would appeal. Rajab, who heads the Bahrain Centre for Human Rights, has been in custody since June 6 on charges of insulting members of the Sunni community on Twitter, days after he was released on bail after a month behind bars over other charges. Amnesty International called for Rajab\'s immediate release, decribing his sentence as \"a dark day for justice in Bahrain.\" The rights watchdog said \"this latest verdict marks the end of the facade of reform in Bahrain\" and condemned its \"blatant ruthless tactics of suppressing dissenting voices\". Rajab led anti-government protests following a brutal crackdown on Shiite-led demonstrations against the regime in March 2011. The activist has insisted on demonstrating inside Manama, unlike the main Shiite opposition which now stages protests in villages, after last year\'s clampdown on protesters who occupied the capital\'s Pearl Square for a month. The court on Thursday also adjourned to August 23 an appeal hearing over Rajab\'s alleged insults to residents of mostly-Sunni Muharaq province, for which he has been sentenced to three months in jail, the lawyer said. The avid tweeter is also accused of insulting the security forces in postings that he admitted came from his account on the microblogging website. The Paris-based International Federation for Human Rights (FIDH) swiftly condemned the latest sentence against Rajab. \"Arbitrarily imprisoning human rights defenders will not stop the people from aspiring to freedom and democratic change,\" said FIDH president Souhayr Belhassen. Bahrain has come under strong criticism from international rights organisations over last year\'s crackdown on demonstrations that were inspired by the Arab Spring uprisings.