Saudi Arabia is putting 30 people on trial on charges of allegedly spying for Iran, media reported Monday.
Those facing trial include an Afghan and Iranian, newspaper al-Hayat reported.
The mass arrest comes as Saudi Arabia, a Sunni monarchy, and Iran, led by Shiite clerics, deepen their regional rivalry, including backing opposition sides in the Syrian and Yemeni conflicts.
Saudi Arabia has long faced unrest among its Shiite minority, which charges that the government discriminates against them in all aspects of life, including economically and religiously.
Al Arabiya news channel said all 30 of the defendants were from the al-Qatif region, in the east, which is predominately Shiite.
The charges against the group include plotting with Iranian intelligence against the kingdom, and that some of the alleged spies met with Iran's Supreme Leader Ali Khamenei. They are accused of high treason.