A Bahrain court on Thursday sentenced prominent Shiite rights activist Nabil Rajab to three years in prison over "unauthorised" protests against the Sunni Al-Khalifa monarchy, a lawyer said.

"The court has sentenced Nabil 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 that 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 via Twitter, only days after he had been released on bail on after a month behind bars over other charges including protests. 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 avid tweeter is also accused of insulting the security forces in postings that he admitted came from his account own on the microblogging website.

Bahrain came under strong criticism from international rights organisations over last year's crackdown on demonstrations that were inspired by the Arab Spring uprisings.