Security forces on Monday detained dozens of men who had staged a protest near a prison in central Saudi Arabia to press for the release of relatives, demonstrators and a rights activist said.
The arrests were made after police had confined the protesters, who included women and small children, to a desert area outside the prison where they were kept without food or water for nearly a day, protesters and activists said.
It was a rare demonstration in the world's biggest oil exporter, where protests are banned.
Saudi Arabia, which has been a target for al Qaeda attacks, say the protesters' relatives are all being held on security grounds. But activists say some are also held for purely political activity and have never been charged.