A Catholic priest has been injured after having acid thrown over him in Zanzibar City, only a month after two British girls were targeted in a similar attack.

Cleric Joseph Anselmo Mwagambwa had just left an internet café when the assailants struck, said police.

"A few minutes later he came back screaming and begging for help," said Rukia Abbasi, who works in the café.

"We gave him water and rushed him to hospital."

"He sustained burns in his face and shoulders. The acid burnt through his shirt," Zanzibar police spokesman Mohamed Mhina told Reuters, and said that the priest was undergoing emergency treatment in hospital.

Police said that no one had been arrested in connection with the attack.

The assault happened in the Stone Town area of the city, where gap-year voluntary workers Katie Gee and Kirstie Trup, both 18 and from London, had acid thrown in their faces by a motorcyclist.

Zanzibar's President Ali Mohammed Shein said the assault had "brought chaos and confusion to our country and outside", and officials offered a £4,000 ($6,000) reward for information leading to the arrest of the perpetrators.

So far, people have been questioned by police over the assault, but no-one has been charged.

The teenagers were flown to the UK for treatment, where they received skin grafts.

In recent months, there have been heightening tensions between the majority Muslim population and Christians on the semi-autonamous Zanazibar archipelago, as well as on mainland Tanzania.

In November, a Muslim leader was injured in an acid attack and two Christian priests were killed. Churches have also been torched.

Friday's assault was the fifth acid attack on the island in that period.

Some have blamed Zanzibari separatist organisation Uamsho (Awakening) for the unrest.

The group wants to break Zanzibar's political union with secular Tanzania, and impose Sharia law.