Theresa May has called on leading international powers to do more to ensure foreign fighters who travel to join Islamic State in Syria and Iraq are brought to justice.
Leading a session on counter-terrorism at the G7 summit in Taormina, Sicily, the Prime Minister said they needed to be prepared to share their expertise with the countries the fighters travel to and fight in.
A senior government source said she made the point that it was important to ensure those countries had the legal means to prosecute, deport or extradite suspects as appropriate.
The Prime Minister warned that as the fighters returned to their home countries, they posed a new terrorist threat.
She called on the G7 members to provide legal and policing support to countries such as Iraq to help them prosecute any foreign fighters they capture.
Mrs May said: “It is vital we do more to co-operate with our partners in the region to step up returns and prosecutions of foreign fighters.
“This means improving intelligence-sharing, evidence gathering and bolstering countries’ police and legal processes.”
Mrs May said G7 members needed to be able to share data securely on foreign fighters so they can be tracked as they cross borders and decisions made on whether they should be arrested.
This would include sharing the identities of foreign fighters who may try to pass through third countries on their way back home.
When evidence was found of illegal activity involving British fighters, she said it should be passed on to the relevant UK authorities so those individuals could be prosecuted on their return.
Mrs May also defended her record on tackling violent extremism as she welcomed backing from the world’s leading industrial nations for new measures to prevent online radicalisation by Islamic State.
In the wake of the suicide bomb in Manchester, leaders of the G7 states agreed a package of measures to step up pressure on tech giants such as Google and Facebook to take down harmful content.
Mrs May said: “We agreed that the threat from Daesh [another name for IS] is evolving rather than disappearing. As they lose ground in Iraq and Syria, foreign fighters are returning and the group’s hateful ideology is spreading online.
“Make no mistake, the fight is moving from the battlefield to the internet. I am clear that corporations can do more. Indeed, they have a social responsibility to now step up their efforts to remove harmful content from their networks.”
The agreement included support for companies to develop tools to identify and remove harmful materials automatically and to report damaging content to the authorities while blocking the users responsible for spreading it.
The G7 also agreed a range of measures to return and prosecute foreign fighters, and to cut off sources of terrorist finance.
In the face of questions over whether more could have been done to prevent the Manchester attack, Mrs May defended her record on the issue when she was home secretary.
“I excluded more hate preachers from the UK than any other home secretary has done before. We didn’t hesitate in protecting our national security,” she said.
In their joint statement, the G7 leaders said they were “united in expressing our deepest sympathy and condolences to the families of the victims of the brutal terrorist act in Manchester”, adding: “We condemn in the strongest possible terms terrorism in all its forms and manifestations.”
Mrs May was due to return to the UK late yesterday.