There is no evidence that three east London girls, thought to be heading to Syria to join terror organisation Islamic State, were radicalised at their Bethnal Green Academy, their principal has said.

As the hunt for the teenagers – Shamima Begum, Amira Abase, both 15, and Kadiza Sultana, 16 – continues, Mark Keary told a press conference pupils could not access Twitter or Facebook on school computers.

“Police have advised us there is no evidence radicalisation took place at the academy,” Mr Keary said.

Reading a statement, he said: “We are all shocked and deeply saddened by the news that three of our students have been reported missing from home, they boarded a flight to Istanbul from Gatwick Airport last week, and our thoughts are with the families of the missing girls at this time.

“This situation follows an earlier disappearance of a student in December of last year.

“The police spoke to that student’s friends at the time and further to this, they indicated that there was no evidence that the girls were at risk of being radicalised or absconding.”

Mr Keary said it was business as usual for the 1,200 pupils and staff who were returning after half-term, although “a full programme of briefing sessions” with police and counter-radicalisation groups was available.

“We operate an outstanding system of pastoral care and personal support, which aims to ensure that all students are comfortable addressing any issues or concerns to members of staff.”

One of Shamima’s sisters, Renu Begum, said she hoped her sister had gone to Syria to bring back the girl who had gone there from Bethnal Green Academy in December.

Ms Begum said Shamima and her friends were “young” and “vulnerable” and if anyone had tried to persuade them to go to Syria it was a “cruel and evil” thing to do.

Girls at Gatwick Airport
Shamima Begum, 15, Kadiza Sultana, 16, and another 15-year-old girl captured on CCTV at Gatwick Airport

Amira’s father, Abase Hussen, said: “The message we have for Amira is to get back home. We miss you. We cannot stop crying. Please think twice. Don’t go to Syria.”

In an appeal to Kadiza, her sister, Halima Khanom, said: “Find the courage in your heart to contact us and let us know that you are safe and you are OK. That is all we ask of you.”

In other developments, Prime Minister David Cameron said he was “horrified” by the girls’ disappearance.

He announced that Home Secretary Theresa May and Transport Secretary Patrick McLoughlin would be working with airlines on new arrangements to ensure children who are at risk are properly identified and questioned. The teenagers had boarded the flight t Istanbul without being asked questions.

The Prime Minister said: “All of us have been horrified by the way that British teenagers appear to have been radicalised and duped by this poisonous ideology of Islamist extremism while at home on the internet in their bedrooms.

“They appear to have been induced to join a terrorist group that carries out the most hideous violence and believes girls should be married at nine and women should not leave the home.

“Their families are understandably heartbroken – and we must do all we can to help.”