Saudi security forces have arrested several Shiites across the kingdom including two clerics over the past days for unspecified reasons, rights activists said on Tuesday. The arrests include doctor Abbas al-Abbad, who works at the Specialist Hospital in Riyadh, university professor Ali al-Haji and banker Ahmed al-Nasser, said the activists. The three who were arrested in the capital are originally from the Al-Ahsa city, in Eastern Province, where the kingdom\'s Shiite minority is concentrated. Security forces also simultaneously arrested Ibrahim al-Humaidi in the capital, and his brother Hussein in the town of Sihat, also in Eastern Province, the sources said requesting anonymity. In the western city of Jeddah, police arrested Shiite cleric Mohammed al-Atiyah, while cleric Badr Al Taleb, from Sihat, was arrested in the Muslim holy city of Mecca, also in the western region, activists said, adding that another Shiite Abdullah Khamis was arrested in Ahsa. Police were not reachable for comment. Since early 2011, mainly Shiite towns in Eastern Province have seen sporadic protests and confrontations between police and Shiite residents who complain of marginalisation. There are an estimated two million Shiites in the Sunni-dominated kingdom of around 27.5 million people. Saudi King Abdullah on January 14 appointed Prince Saud bin Nayef as the new governor of Eastern Province, replacing Prince Mohammed bin Fahd who was in office since 1985 but was strongly criticised by Shiite activists for his aggressive policy towards them. Prince Saud\'s appointment was welcomed by Shiite dignitaries in Eastern Province.