Saudi security forces have detained nine people accused of instigating riots in the eastern region of Qatif.
Interior ministry spokesman Maj Gen Mansour al-Turki said they were Saudi nationals and had been arrested at a house used as one of their hideouts.
Earlier this month, a Shia protester was shot dead in clashes with security forces in the Qatif town of al-Awamiya.
Many Shia have attended demonstrations recently to complain of discrimination by the Sunni-dominated authorities.
An interior ministry statement carried by state media said the nine people arrested on Monday evening had been involved in two attacks on 14 and 18 January, in which "three members of the security forces were wounded".
Security forces killed the protester al-Awamiya on 13 January. Activists said people had only been throwing stones, but officials said a security vehicle had been shot at and attacked with petrol bombs.
Qatif, in the oil-rich Eastern Province, is home to a Shia majority that has long complained of marginalisation at the hands of the Sunni ruling family, the Al Saud.
Protests erupted in Eastern Province in March when the popular uprising in neighbouring Bahrain, which has a Shia majority and a Sunni royal family, was crushed with the assistance of Saudi and other Gulf troops.
In November, four Shia men were shot dead by security forces over four days in Qatif. The interior ministry said they had been armed and operating on "foreign orders" - code for Iran.
About 400 people have been arrested since March. Activists say 70 remain in custody, including author Nazir al-Majid and human rights activist Fadil al-Munasif.