Two British women who had acid thrown in their faces in Zanzibar are expected to arrive back in the UK later.
Kirstie Trup and Katie Gee, both 18 and from London, were taken to hospital in mainland Tanzania after being attacked in the east African island's capital.
It is believed they left Tanzania on a flight to the UK on Thursday night.
Their mothers, Rochelle Trup and Nicky Gee, said they were "extremely upset" by the "completely unprovoked attack" carried out by two men on a moped.
Police said acid was thrown on the teenagers' faces, chests and hands as they walked through the streets of Stone Town, the old part of the island's capital Zanzibar City, on Wednesday evening.'Lovely daughters'
Reporting from the scene, the BBC's Alastair Leithead said the attackers sped away after the incident, and police do not know why the women were targeted.
The women's mothers said in a statement issued on Thursday: "Both families are extremely upset and distressed at this completely unprovoked attack on their lovely daughters who had only gone to Zanzibar with good intention.
"We appreciate all the interest and support we have received from the media but we would ask that we are left alone until we have been reunited with our daughters."
Nicky Gee told Sky News her daughter's body and whole face had been burned by acid.
The victims were two weeks into a three-week trip booked through the company i-to-i Travel, which said it was focused on getting them back to the UK.
Kari Korhonen, co-director of Art in Tanzania, the charity the women had been volunteering for, said they were "OK considering the seriousness of this type of case".
Another spokesman for the charity said they had been on their way to dinner when the attack happened.
Police on Zanzibar said it was the first time foreigners had been attacked in this way.
Deputy police commissioner Mkadam Khamis told AFP news agency: "The motive for the attack...has not been established. Investigations are [continuing] until we apprehend the criminals."
The Foreign Office said it was concerned to hear of the attack and was providing consular assistance.
The BBC's Tulanana Bohela, in Dar es Salaam, said Islam is the main religion on Zanzibar and in more remote parts of the island, away from tourist beaches, there are signs asking foreigners to respect the local culture and cover up - in case skimpy outfits upset villagers.
However, most islanders depend on tourism for their livelihoods and are happy to see tourists and there is little antagonism towards them, she said.'Economic pillar'
Tanzania's President Jakaya Kikwete visited the women at the Aga Khan Hospital in Dar es Salaam, the country's largest city, and promised that the men responsible for the "shameful" attack would be found.
Tanzania's minister of information, tourism, culture and sports, Said Ali Mbarouk, said: "I beg our nationals, this is not something they should be doing.
"Tourism is the strongest pillar of our economy, so if we do such acts we are killing our economy, and our livelihoods in general.
"So it is not an honourable thing to do, it's a bad thing and it should be condemned by all citizens of Zanzibar."
The Foreign Office's travel advice says 75,000 British nationals visit Tanzania - including semi-autonomous Zanzibar - every year and most have "trouble free" visits.
But it warns that "violent and armed crime is increasing" and "there is an underlying threat from terrorism".
It also says "mugging, bag snatching (especially from passing cars) and robbery have increased throughout the country" and "in Zanzibar incidents have taken place in Stone Town and on popular tourist beaches".
Recent attacks in Zanzibar include an acid attack on a Muslim cleric in November, and the shooting dead of a Catholic priest in February. Another priest was shot and wounded in December