Saudi police have arrested 176 people, including 15 women, for holding an illegal protest to demand the release of Islamist prisoners. The agency, quoting a police spokesman, said protesters were arrested "after refusing to break up a gathering outside the offices of the investigation bureau and the prosecution in Buraida," in central Saudi Arabia. The spokesman accused the protesters of acting on behalf of "deviant groups" -- a term the authorities usually use to refer to the Al-Qaeda jihadist network. Demonstrations are banned in Saudi Arabia, an ultra-conservative Muslim kingdom that has remained relatively untouched by the Arab Spring uprisings. Small groups of women have gathered almost daily in Buraida, north of Riyadh, to demand the release of imprisoned Islamist relatives, and dozens of protesters held a rare sit-in outside the Buraida prison in September. At the time police dispersed the protesters and authorities later warned they would deal "firmly" with demonstrations, sparking condemnation from Amnesty International which urged Riyadh to withdraw its threat.