CIA Director John Brennan warned on Monday that the attacks in Paris claimed by the extremist Islamic State movement were not a “one-off event” and that the militants may have similar operations ready to launch.

Foiling those plots, however, could prove difficult because Europe’s intelligence and security resources are severely stretched trying to keep track of the hundreds of European extremists who have returned home from fighting in Syria and Iraq.

“A lot of our partners right now in Europe are facing a lot of challenges in terms of the numbers of individuals who have traveled to Syria and Iraq and back again, and so their ability to monitor and survey these individuals is under strain,” Brennan said.

Brennan’s comment at a Washington policy institute came as France, Belgium and other countries intensified a manhunt for suspects in Friday’s attacks on a concert hall, sports stadium, restaurants and bars in Paris that killed 129 people.

Read the article “CIA Chief Warns Islamic State May Have Other Attacks Ready” on reuters.com.