Two British teenagers who were attacked with acid on Zanzibar returned home today as five men were being questioned by police on the Indian Ocean island.

Volunteer teachers Katie Gee and Kirstie Trup, both aged 18, flew in to RAF Northolt in London to be reunited with their families. The women had been attacked by men on a motorcycle as they walked along a road in the island’s main city, Stone Town, on Wednesday night. Both suffered burns to their faces, chests and hands.

Katie thanked supporters for their good wishes with a post on Twitter which said: "Thank you for all your support x".

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The student sent the message from Chelsea and Westminster Hospital in London where she and her friend were receiving treatment for their burns inflicted in an unprovoked attack while they were on a volunteering holiday.

Zanzibar police have offered a reward of 10m Tanzanian shillings (£3,970) for information leading to the capture of the attackers.

The teenagers were taken to the burns unit where consultant surgeon Andy Williams said: “We’re still assessing their injuries. Both girls are well and their families are with them.”

Earlier yesterday Katie’s mother, Nicky Gee, 45, said: “I am just glad she is home. I want to get inside and see her. We spoke this morning and she said she was OK. It has been a terrible ordeal.”

Marc Trup, Kirstie’s father, described the girls as being “inconsolable”. He said: “We couldn’t get anything out of them because they had been burnt. Both girls are very shocked and very frightened. She [Kirstie] can still see and she is not dead. Whatever it is we will cope with it.”

The victims, both from London, were two weeks into a three-week trip as volunteer teachers for the charity Art in Tanzania.

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Mr Trup said the girls were dressed appropriately and had been warned not to wear anything that gave away their Jewish background, including the Star of David. “We know it’s a Muslim country, they were Western girls. Unfortunately they went out during the month of Ramadan,” he said. “There has been a huge alert in African countries with potential threats. Maybe it’s connected, maybe not.”

Mkadam Khamis, regional police commissioner in Zanzibar, said five people had been brought in for questioning but they had not yet been arrested. “There are five people we have, all men, who we are interrogating over this matter this morning,” he said. “They have not yet been arrested. They are co-operating and answering our questions. Later today maybe there will be a development legally.”

Jaf Shah, the executive director of Acid Survivors Trust International, based in London, told The Independent of his surprise at the attacks: “I am actually quite surprised, simply because I don’t think I could ever recall a tourist or aid worker being attacked by acid. So that in itself is quite unusual. The fact that Zanzibar is very reliant on the tourist industry for its income also adds an additional surprise to the attacks. I’m also not aware of any attacks taking place in Zanzibar in the past.” Mr Shah added that acid attacks in East African countries were not uncommon. In Uganda there were 35 reported acid attacks in 2011.

The girls had originally planned to return in time to collect their A-Level results next week, with Ms Trup hoping to study history at the University of Bristol and Ms Gee considering the University of Leeds.

Ms Gee had been attacked previously on the island. A friend, Oli Cohen, 21, told The Daily Telegraph: “Katie was attacked two weeks ago by a Muslim woman for singing during Ramadan. She was shocked as it just came from out of the blue – but she wasn’t scared enough to come home. She stayed out there to finish her volunteering.”

Video: Britons attacked with acid