British police have briefed students at an east London school attended by three girls believed to be travelling to Syria, their headmaster said on Monday.
Mark Keary said the police were part of a "support team" including experts in de-radicalisation from the British government's Prevent programme called in following the girls' disappearance last week.
Keary told reporters in a briefing at the Bethnal Green Academy that the police had indicated there was "no evidence that radicalisation of the missing students took place at the academy".
"It is clear that this is an international issue which is increasing in severity and it's affecting schools across the country and beyond," Keary said.
Kadiza Sultana, 16, and 15-year-olds Shamima Begum and Amira Abase left their homes last week and flew to Istanbul, raising concerns they would travel on to Syria to join Islamic State jihadists.
Around 500 British nationals are believed to have travelled to Iraq and Syria to join the IS group.
Sultana and Begum are British nationals, while Abase is a German citizen.
The three were all friends with another student at the school who left for Syria in December, one of some 550 Western women believed to have gone to Syria.
"Our priority is to provide a business as usual approach for our 1,200 students and staff," Keary said.
Police have made an unprecedented appeal for the girls to come home along with their families and the case has sparked a heated debate over whether officers could have acted sooner and whether warning signs were missed.
Keary said the school had "an outstanding system of pastoral care" and restricted access for students to Facebook and Twitter on its computers.
Someone using a Twitter account in Begum's name last Sunday seems to have contacted Aqsa Mahmood, a woman from Glasgow, Scotland who reportedly travelled to Syria last year to marry an IS group fighter.
"A core aspect of our ethos is to promote the British values of democracy, tolerance and respect, particularly respect for other cultures," Keary said.
Britain has prosecuted people for preparing to join IS and the authorities have seized passports from would-be jihadists under powers that have been reinforced by a new security law passed this month.