The headteacher of the school attended by three teenage girls believed to have travelled to Syria to join Islamic State has said police found no evidence the missing students were radicalised there.

Mark Keary, principal of Bethnal Green Academy, east London, said that they were "shocked and saddened" by the disappearance of Shamima Begum, 15, Kadiza Sultana, 16, and 15-year-old Amira Abase.

Police spoke to the girls after another student disappeared in December and indicated at the time that there was no evidence that they were at risk of being radicalised or absconding, Mr Keary said.

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."

Scotland Yard confirmed last week that the girls were spoken to in December following the disappearance of their friend but said there was nothing to suggest at the time that they were at risk.

Officers are in Turkey as the search continues.

Relatives have made emotional pleas for them to come home.

The girls boarded a flight from Gatwick Airport to Istanbul in Turkey last Tuesday.

Meanwhile, Prime Minister David Cameron has called for airlines and internet companies need to do more to prevent radicalised British teenagers travelling to the Middle East to join Islamic State.

Mr Cameron told MPs he was "horrified" over by the case of three London girls.