Authorities are bracing for potential violence in Tanzania's semi-autonomous island of Zanzibar following Friday prayers.

Zanzibar has seen running clashes between religious groups and police after a Muslim religious leader, Farid Adi, went missing Tuesday night. The government denies any connection to Adi's disappearance.

Police have used tear gas to disperse crowds. One security officer was killed in clashes on Wednesday. Dozens of people have been arrested.