EU Counter-Terror Chief: More Attacks ‘May Happen’

Gilles de Kerchove says there's no such thing as 100% security.

BRUSSELS— -- One of Europe’s top counter-terrorism officials said today that it’s impossible to guarantee 100 percent security and that other attacks could follow last week’s incidents in Paris.

“We know too much how prisons are major incubators of [extremism],” he said.

In the case of the Paris attacks, the gunmen in each assault had spent time in prison together and with other radical figures, an investigation after the attack found.

Rather, Kerchove said disengagement or rehab-like programs could be the answer.

“We will tackle the problem in a significant way, but it is a challenge,” he said.

ABC News' Lee Ferran contributed to this report.