Amnesty International says a Saudi Arabian court has convicted a prominent rights activist of anti-state crimes and sentenced him to four years in prison.

The London-based group says activist Mohammed al-Bajady was tried in secret. He was detained a year ago and is believed to have been on a hunger strike for a month.

Amnesty said in a statement Tuesday that it has "credible information" that a Specialized Criminal Court in Riyadh found al-Bajady guilty of several offenses, including participating in the establishment of a human rights organization and harming the image of Saudi Arabia in media articles.

The group says the verdict was pronounced during a secret court session on April 10 which al-Bajady's lawyers were not allowed to attend.