Leaders of the Group of Seven industrialised nations have decided to tighten defences against the risk of terror attacks by European jihadists returning from the Syrian front.
"We have agreed to intensify efforts to address the issue of foreign fighters travelling to and from Syria," British Prime Minister David Cameron said at the close of a G7 summit.
He said talks were taking place with Syria's neighbours to strengthen their borders in the wake of an attack on the Jewish Museum in Brussels late last month, believed to be the work of a young French jihadist fighter recently returned from Syria.
Almost 800 French citizens are believed to have signed up to fight President Basahar al-Assad's regime and French President Francois Hollande said more than 30 French fighters had already died on the Syrian battlefront.
Hollande added it was essential "to cooperate to prevent, dissuade and punish" foreign fighters "who can undermine our security".
"We have unfortunately just had proof of that," Hollande added in reference to the Brussels attack, the first such incident in the city in three decades.
It is suspected to be the work of a 29-year-old Frenchman, Mehdi Nemmouche, who spent more than a year fighting with radical jihadists in Syria.
The May 24 attack in the heart of Brussels was also raised in talks between US President Barack Obama and Belgian premier Elio Di Rupo.
"We resolve to intensify our efforts to address the threat arising from foreign fighters travelling to Syria," a statement from the seven G7 leaders said.
The Brussels attack killed three people outright and left a fourth clinically dead.
Europe can expect further "small-scale attacks" like the Brussels shooting, the EU's anti-terror chief Gilles de Kerchove said this week.
But with more than 2000 Europeans in Syria or on their way there, receiving military training and becoming more radicalised, the Brussels attack was "very, very worrying" for Europe's future security, he said.
Around 400 British nationals, 320 Germans and 200 Belgians are believed to have left for Syria.
On Thursday, home affairs ministers from nine European nations agreed to step up efforts to identify potential volunteers, slow their departure and track them on return, and share information with each other.
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