Two British teenage girls were being treated for burns at a London hospital on Saturday after acid was hurled in their faces in the Indian Ocean island of Zanzibar. Doctors said Kirstie Trup and Katie Gee, both 18, were doing \"well\" after Wednesday\'s attack, and Gee took to Twitter to thank supporters for their good wishes. The girls, close friends who were working for three weeks as volunteer teachers on Zanzibar, were attacked by two men on a motorbike as they strolled through the historic centre, Stone Town. The island\'s authorities have offered a reward for the capture of those responsible, and police said on Friday that seven people had been questioned. The girls\' families released a photograph of one of the victims\' injuries, showing dark burns seared across her jaw, neck and chest, without identifying her. Trup\'s father, Marc Trup, told The Times newspaper that efforts to help one of the girls after the attack had actually made her injuries worse. One was immersed in the sea, where the salt water soothed the wounds, but the other was doused with dirty water which only made things worse, he said. Gee\'s father, Jeremy Gee, earlier described the burns as \"horrendous\", telling The Daily Telegraph: \"We are absolutely devastated. The level of the burns are beyond imagination.\" The girls, who are due to start university in the coming weeks, were flown to Tanzania\'s economic capital Dar es Salaam for treatment, and then on to London on Friday. In a Twitter message from the Chelsea and Westminster Hospital in the British capital, which has a specialist burns unit, Gee wrote: \"Thank you for all your support x\". Andy Williams, consultant burns and plastic surgeon, said on Friday that the team was still assessing the girls\' injuries. \"Both girls are well and their families are with them. They will be staying at Chelsea and Westminster Hospital,\" he said. \"Both families would like to thank everyone that\'s helped to bring the girls back. The families now wish to have time with the girls.\" Hospital staff in Dar es Salaam said their injuries were relatively minor and suggested the liquid thrown at them may have been diluted acid. Zanzibar\'s Tourism Minister Said Ali Mbarouk offered a reward of 10 million Tanzanian shillings ($6,200, 4,600 euros) for information leading to the arrest of the suspects, describing the attack as \"a shame on the people of Zanzibar\". Tourism is the lifeblood of the semi-autonomous Tanzanian island, which is famed for its pristine white-sand beaches. \"We have to work harder to make sure that Zanzibar is safe for visitors and citizens,\" Mbarouk said. Tanzanian President Jakaya Kikwete, who visited the two girls in hospital in Dar es Salaam, said the attack had \"tarnished the image\" of the country. Tanzania is predominantly Muslim, and the attack happened at the end of the Islamic holy month of Ramadan as people were beginning to celebrate the Eid al-Fitr holiday. Some of the island\'s more conservative Muslims object to foreign tourists who wear revealing clothes, as well as bars selling alcohol. One of the girls had posted on her Twitter page that she had been hit by a Muslim woman in the street earlier in the trip, apparently for singing during Ramadan. There were also reports that the pair had argued with a local shopkeeper. But their families insist they had been careful to dress modestly while out on the streets of Zanzibar. Both from Jewish families, they also avoided any prominent displays of their faith. \"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,\" a spokesman for the girls\' mothers said on Thursday. The girls had been coming to the end of a three-week placement teaching at a local school, organised through i-to-i Travel, a British company that organises gap year work. Acid has been used in several recent attacks in Zanzibar, although this is the first assault of its kind targeting foreigners on the holiday island. Source: AFP