There is no evidence that three teenage girls feared to have travelled to Syria to join Islamic State were radicalised at their east London school, a headteacher said today.

Bethnal Green Academy principal Mark Keary said the disappearance of Shamima Begum, 15, Kadiza Sultana, 16, and 15-year-old Amira Abase had "shocked and sadeened" everyone at the school.

But he said police have found no evidence they were groomed while at the academy, nor were the girls believed to be at risk when officers spoke to them after another student disappeared in December.

He also said that access social media at the school is "strictly regulated". A tweet sent from a Twitter account under Shamima's name was sent to Aqsa Mahmood, who left Glasgow for Syria to be a "jihadi bride" in 2013.

In a statement issued at the school, Mr Keary 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. The police have also confirmed that the families of the missing girls were unaware of their plans to leave the country."

He said students are unable to access Twitter or Facebook on school computers.

"With such measures in place, police have advised us that there is no evidence that radicalisation of the missing students took place at the academy," he said.

Mr Keary added: "From the increasing number of similar news reports around the world, it is clear that this is an international issue which is increasing in severity and it's affecting schools across the country and beyond. We are constantly reviewing our safeguarding procedures."

The school is supporting the police investigation, he said, adding that police have requested that they make no further comment as the inquiry is ongoing.

Officers spoke to staff during briefings today, pupils have attended assemblies with support agencies and a team is on site to speak to students and staff.

Mr Keary said the school, which has been rated as "outstanding" by Ofsted, is "extremely proud" of the "exceptional learning experience" it provides to students.

"A core aspect of our ethos is to promote the British values of democracy, tolerance and respect," he said. "Particularly respect for other cultures and this is taught through a wide variety of curriculum topics and learning programmes.

"We also 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."

Mr Keary reiterated the police appeal, adding: "Our thoughts are with the families of the missing girls as we await news and hope for their safe return to their homes and families."