(CNN) -- Demonstrators protested in Saudi Arabia's Eastern Province on Friday to demand the release of Shiite prisoners they feel are being held unjustly.
An outspoken Shiite prayer leader who demonstrators say was arrested last Friday was a focal point of the "day of rage" protest, said Ibrahim al-Mugaiteeb, president of the Human Rights First Society.
Sheikh Tawfeeq Al-Amer was arrested Friday after a sermon stating that Saudi Arabia should become a constitutional monarchy, al-Mugaiteeb said.
Saudi Arabian authorities could not be immediately reached for comment.
The protest comes on the heels of two similar demonstrations held in the province Thursday, al-Mugaiteeb said, when about 200 protesters in the city of Qatif and 100 protesters in the city of Awamiyya called for the release of Shiite prisoners.
Al-Mugaiteeb said authorities arrested 22 people who participated in Thursday's protest in Qatif.
"We deplore this action by the Saudi security forces," he said.
Another protest took place in Riyadh after Friday prayer, according to two Saudi activists. The sources asked not to be identified because of concerns for their safety.
According to the activists, as many as 40 anti-government demonstrators gathered outside Al-Rajhi Mosque for a short protest. At least one man involved in organizing the protest was arrested by Saudi police, the activists said.
The activists said the protesters attracted a crowd of worshipers leaving the mosque. Some of the protesters carried signs showing a map of Saudi Arabia that did not contain the words "Kingdom of Saudi Arabia," a clear affront to the Saudi royal family.
Saudi Arabia has cracked down on protests in the past.
Shiites are a minority in Saudi Arabia. They live primarily in the Eastern Province -- where many major oil companies operate.
The protests come as sectarian violence between Shiites and Sunnis flares in neighboring Bahrain.
Analysts believe protests in Bahrain could spill over into Saudi Arabia's oil fields, located mostly in Shiite provinces.
After three months abroad for medical treatment, Saudi Arabia's King Abdullah returned home late last month to a Middle East shaken by unrest, and announced a series of sweeping measures aimed at relieving economic hardship and meeting with Bahrain's beleaguered monarch.
The Saudi government released three Shiite political prisoners ahead of the king's return.