A man visible on a cell block's control room monitor, pacing in his small cubicle in a gray robe, is one of a rising number of security prisoners in Saudi Arabia, as war has sparked a surge in domestic jihadist activity.

Until last year, the population of inmates at facilities like Ha'er Prison had been dropping as those detained during an al-Qaida uprising a decade ago were gradually released.

But as anger has grown in the kingdom over what many Saudis see as oppression of their fellow Sunnis by Shiite Muslims in Syria and Iraq, an increasing number of young Saudis have sworn to help by taking up arms themselves.