The Islamic State extremist group poses a rising threat amid political instability in West Africa and the Sahel and remains intent on carrying out attacks abroad, the U.N. counter-terrorism chief said Thursday.

Vladimir Voronkov reiterated U.N. findings that IS continues to pose a significant threat to international peace and security, especially in conflict zones, despite significant progress by U.N. member nations in countering the threat. The group has also increased operations in its former strongholds in Iraq and Syria as well as Southeast Asia, Voronkov said.

Voronkov told the U.N. Security Council that in West Africa and the Sahel, a broad region cutting across the continent, the situation has deteriorated “and is becoming more complex,” as local ethnic and regional disputes cross with the agenda and operations of the extremist group, which is also known by its Arabic name Daesh, and its affiliates.

“Daesh affiliates continued to operate with increasingly more autonomy from the Daesh core,” he said, warning that if this trend persists there is a risk “that a vast area of instability may emerge from Mali to the borders of Nigeria.”