The most recent, earlier this month, saw a police officer killed, roads blocked and shops closed across Stone Town.
The Association for Islamic Mobilization and Propagation, also known by the acronym Uamsho, has been behind the unrest, urging the Zanzibar archipelago's independence fro the Tanzanian mainland.
One of Uamsho's slogans, "if the coat doesn't fit, take it off", refers to the breakup of the United Republic of Tanzania, which was originally formed by the 1964 union of Zanzibar and the mainland area of Tanganyika.
Established as an Islamic NGO in 2001, Uamsho has become increasingly radicalized, gaining support among disappointed supporters of Tanzania's current largest opposition party, Civic United Front, which formed a government of national unity with Tanzania's ruling party, Chama Cha Mapinduzi two years ago, the U.N. Integrated Regional Information Networks news agency reported.