A prominent human rights activist in Bahrain has been sentenced to three consecutive year-long sentences for participating in what the courts characterized as "illegal gatherings," referring to activities connected to the country's ongoing popular uprising.

Nabeel Rajab, the president of the Bahrain Center for Human Rights, has already been serving a three-month prison sentence since July after posting comments on social media websites, calling for Bahraini Prime Minister Sheikh Khalifa bin Slaman al-Khalifa to step down.

Rajab's lawyer Mohammed al-Jish said he would appeal the most recent ruling, while an appeal for his three-month sentence has been postponed until August 23.

Rajab has been a one of the main protest organizers within the small Gulf island nation's pro-democracy movement that began in February during the wave of Arab Spring uprisings.

Pro-democracy activists have called for an end to Bahrain's constitutional monarchy under King Hamad and demanded that the constitution be written to expand social, political and economic freedoms for Bahraini citizens.

The Bahraini government has responded with violent suppression of protests by police forces and widespread censorship across online and traditional media platforms.