Relatives of Saudi prisoners - most of them held without charge - have held a rare protest urging their release.
More than 100 people, including women and children, have taken part in the sit-in that began on Sunday outside a desert prison in Qassim province.
Riot police used force to break it up, arresting several protesters, according to activists.
They say a similar protest has begun outside the office of the Human Rights Commission in the capital, Riyadh.
One of the protesters in Qassim, Rima Jureish, told AFP news agency that her husband had been "detained for more than nine years without charge".
King Abdullah has introduced economic and social reforms during his seven-year reign, including moves to improve the position of women, but correspondents say he has left Saudi Arabia's political system untouched.