DAR ES SALAM (Reuters) - Fifteen people, including suspected Islamist militants and individuals linked to an acid attack on a clergyman, have been arrested in Tanzania's semi-autonomous Zanzibar islands, a senior police officer said.
The Indian Ocean islands are growing headache for the Tanzanian government as they struggle with religious tensions and deep social and economic divides.
Friday's acid attack on a Roman Catholic priest came a month after two men threw a corrosive liquid over two British teenagers in Zanzibar, an attack that hit Tanzania's image as a tourist-friendly destination.
"Fifteen people have been arrested in police raids on criminal networks," Zanzibar's police commissioner, Mussa Ali Mussa, told Reuters. "Among them are suspected members of al Shabaab, suspects behind the recent acid attack on a Roman Catholic priest and unlicensed acid distributors."
All those arrested on Sunday were Tanzanian nationals, Mussa added.
Al Shabaab is an al Qaeda-allied group that has been fighting the Western-backed government in Somalia, around 500 km (310 miles) north along Africa's coast from Zanzibar.
Mussa did not say what the suspected militants were doing on the archipelago, though he said they were not linked to the acid attacks.
As in neighbouring Kenya, many Muslims living along Tanzania's coast feel marginalised by the secular government and both countries have been fertile recruitment grounds for the Islamist groups.
Mussa said prosecutors were close to laying charges against two other men detained in connection with the attack on Britons Katie Gee and Kirstie Trup. The young women suffered facial, chest and back injuries.
Tanzanian President Jakaya Kikwete has warned that religious tensions threaten peace in the nation of 45 million people.
Two Christian leaders were killed in Zanzibar earlier this year in separate attacks and there have been arson attacks on churches.
A separatist group in Zanzibar, Uamsho (Awakening), has been blamed by some but authorities have not linked the group to the violence.
Uamsho wants the archipelago to end its 1964 union with mainland Tanzania, which is ruled as a secular state, and wants to introduce Islamic Sharia law in Zanzibar.