Zanzibar, Tanzania (CNN) -- Two young British women were injured in an acid attack carried out by two men on a motorcycle on the east African island of Zanzibar, local police said Thursday.
The women, who were attacked in Stone Town, the island's historic center, had been working as volunteer teachers on the island, travel firm i-to-i Travel said.
Stone Town is a UNESCO World Heritage Site popular with tourists.
The Zanzibar government and a spokesman for the women's families identified the victims as Katie Gee and Kirstie Trup, both 18.
The attack occurred Wednesday night as the women were walking unaccompanied along a street, said police Cmdr. Muccadam Khamis. The attackers, who did not take anything from their victims, left the scene on the motorbike, he said.
Eyewitnesses said the acid was splashed on the women's faces, chests and hands.
The government condemned the attack and vowed to find the perpetrators.
"The event is a great tragedy, and an attack of this nature against a foreign citizen, has never happened here before," the Zanzibar government said in a statement.
The government also said it would regulate the purchase of acid and other related products, and warned that such attacks could seriously damage the island's tourism industry, one of its main sources of funds. Police patrols will be stepped up in major tourist spots, officials promised.
The women were given first aid treatment at a local medical center before British consular officials helped them reach a hospital in the city of Dar es Salaam, on the Tanzanian mainland, Khamis said.
The UK Foreign Office is providing consular assistance and is in contact with the Tanzanian authorities, a spokesman said.
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The women, who were in the final week of their trip when they were attacked, have been discharged from the hospital in Dar es Salaam, i-to-i Travel said in a statement.
"The motive for the incident is as yet not known and we will await the report from the local authorities in Zanzibar before any comment can be made," a company statement said.
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"The safety of our customers is of paramount importance to us and our own investigation will be launched as soon as it is possible to do so."
Gee and Trup, both from London, are expected to fly out from Zanzibar on Thursday evening bound for the United Kingdom, the agency said.
The women's families asked for privacy until they're reunited with their daughters.
"Both families are extremely upset and distressed about this completely unprovoked attack on their lovely daughters who had only gone to Zanzibar with good intention," relatives said in a joint statement.
No one has claimed responsibility for the attack but it comes against a backdrop of rising extremist Islamist sentiment in the area.
Last month, Tanzanian media reported that a businessman of Arab origin who had built a mall close to the American Embassy in Dar es Salaam was also injured in an acid attack. He is believed to be in South Africa for treatment.
Zanzibar is a semi-autonomous part of Tanzania, a nation of just over 48 million people.
According to the CIA World Factbook, the population of Zanzibar is 99% Muslim, while the residents of mainland Tanzania are split roughly evenly among Christian, Muslim and indigenous beliefs.
British authorities have said tens of thousands of British holidaymakers travel to Zanzibar every year and that this is the first such incident to affect foreign visitors to the island.
i-to-i Travel says it aims to provide young travelers with "meaningful travel trips" and life-changing experiences by placing them as volunteers with community projects overseas run by non-governmental organizations.
Its website advertises trips lasting from two to eight weeks teaching English in Stone Town.