Al-Wefaq said in a statement on Saturday the group “can confirm that Sheikh Ali Salman has been arrested.”
"He is in detention after a series of illegal measures which comprised summonsing him to the office of criminal investigation and bringing him before a public prosecutor," it added.
The group also said in a separate statement that people have gathered outside Sheikh Salman’s house in Bilad al-Qadeem – a suburb of the capital, Manama – protesting his arrest.
It added that the protesters held pictures of Sheikh Salman, “demanding his immediate release.”
Police reportedly fired shots to disperse the protesters.
Bahrainis have been staging demonstrations since mid-February 2011, calling for political reforms and a constitutional monarchy, a demand that later changed to an outright call for the ouster of the ruling Al Khalifa family following its brutal crackdown on popular protests.
Bahrain’s main opposition groups, al-Wefaq and the National Democratic Action Society (NDAS), have blamed the regime for lacking political will to carry out reforms.