(CNN) -- Tanzanian police have arrested 15 suspects following the latest acid attacks on the island of in recent months.
Most of the suspects arrested Tuesday had acid in their possession and experience working with it, said Mussa Ali Mussa, a local police commissioner.
Attackers hurled acid at a Catholic priest as he was leaving an internet cafe last week, the third such unprovoked assault in two months.
The Rev. Joseph Anselmo Mwagambwa, who was attacked Friday in Zanzibar, is undergoing treatment at the mainland city of Dar es Salaam.
Katie Gee and Kirstie Trup, both 18, were attacked in Stone Town, the island's historic center. They had been working as volunteer teachers on the island.
In another incident in July, a businessman who had built a mall close to the American Embassy in Dar es Salaam was also injured in an acid attack, Tanzanian media reported.
The attacks occurred at a time when Islamist extremism is escalating in the area, which has a Muslim majority. The government has said it will consider regulating the purchase of acid and other related products, and warned such attacks will damage the island's tourism industry.
Zanzibar is a semiautonomous part of Tanzania.
CNN's Larry Register and journalist Farouk Karim contributed to this report