Two Jewish British teenage girls arrived home on Friday, badly burned after acid was hurled in their faces in Zanzibar, while the island’s authorities offered a reward for the capture of their attackers.

AFP reported that Katie Gee and Kirstie Trup, both 18, were flown to a Royal Air Force (RAF) base in London and were taken straight to a hospital for further treatment.

The teenagers, both Londoners who had been working as volunteer teachers in Zanzibar, were attacked on Wednesday by two men on a motorbike, in the first such attack on foreigners on the Indian Ocean island.

The girls’ families have released a photograph of one of the victims’ injuries, showing dark burns seared across her jaw, neck and chest, reported AFP.

Television pictures showed two ambulances driving to meet a private jet at the RAF Northolt base in west London.

The girls, close friends who were due to start university in the coming months, were taken straight to the Chelsea and Westminster Hospital’s burns unit.

In a statement outside the hospital, Andy Williams, consultant burns and plastic surgeon, said the team were still assessing their injuries.

“Both girls are well and their families are with them. They will be staying at Chelsea and Westminster Hospital.

“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,” he added, appealing for privacy “at this difficult time”.

Katie’s father Jeremy Gee earlier described the burns as “horrendous”.

“We are absolutely devastated,” he told The Daily Telegraph newspaper. “The level of the burns are beyond imagination.”

Marc Trup, Kirstie’s father, said the girls were “inconsolable”.

Hospital staff in Tanzania’s economic capital of 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) for information leading to the arrest of the suspects.

He described the attack as “a shame on the people of Zanzibar,” according to AFP.

“We have to work harder to make sure that Zanzibar is safe for visitors and citizens,” Mbarouk said.

Seven people have already been questioned over the attack, according to Zanzibar police.

Tanzanian President Jakaya Kikwete, who visited the two young women in hospital after they were flown from the island to Tanzania’s largest city 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.

Their families insist they had been careful to dress modestly while out on the streets of Zanzibar, and to avoid any prominent displays of their Jewish heritage.

“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 in a statement quoted by AFP.

The girls were attacked as they strolled through Stone Town, Zanzibar’s historic center.

They had been coming to the end of a three-week placement teaching at a local school, organized through i-to-i Travel, a British company that organizes gap year work.