The top U.N. envoy for Syria told the Security Council on Monday that the threat of terrorism is “resurging” with attacks by Islamic State extremists set to double this year, endangering civilians already facing a “protracted state of displacement and dire humanitarian conditions.”

U.N. Special Envoy Geir Pedersen said Syria is “riddled with armed actors, listed terrorist groups, foreign armies and front-lines” 13 years after President Bashar Assad’s crackdown on peaceful protests against his government turned to civil war. Nearly a half million people have died in the conflict and half the country’s pre-war population of 23 million has been displaced.

The Islamic State group declared a self-styled caliphate in a large swath of territory in Syria and Iraq that it seized in 2014. It was declared defeated in Iraq in 2017 following a three-year battle that killed tens of thousands of people and left cities in ruins, but its sleeper cells remain in both countries.