Bahrain Mirror (Reuters): A Shi'ite opposition leader already serving a four-year jail sentence in Bahrain has been accused of three more offences including "public incitement against the constitutional order of the country", his lawyer said on Sunday.

The public prosecutor's office said it was investigating content on the social media account of Ali Salman, who was convicted last year of inciting unrest, and had questioned him in the presence of three lawyers.

The charges also include not complying with laws and calling for unauthorized marches. "The public prosecution formally charged him with these accusations," one of Salman's lawyers, Hassan Radhi, said, adding that the charges carried sentences of six months to three years.

The Sunni Muslim-led island kingdom, which hosts the U.S. Fifth Fleet, has experienced sporadic unrest since mass protests in 2011 led by majority Shi'ites demanding reforms and a bigger role in government. The government denies opposition charges it discriminates against Shi'ites.

The prosecutor's office said Salman, the most senior jailed figure in the Shi'ite opposition, had denied the charges. It was not immediately clear who was running his Twitter account while he was in prison.

Bahrain says the opposition has a sectarian agenda and is backed by Shi'ite power Iran, a charge Shi'ite groups deny.