The head of the United Nations Office against Terrorism told the UN Security Council on Tuesday that countering the threat of foreign terrorist fighters returning from Iraq and Syria requires international cooperation.

More than 40,000 combatants from over 110 countries had joined terrorist groups fighting in Syria and Iraq, with some 5,600 fighters from 33 nations now returned home, Vladimir Voronkov said.

Others have traveled elsewhere, moving from Islamic State military defeats in those two nations to Libya and other countries, including Yemen and Afghanistan.

Voronkov was joined by Executive Director Michÿle Coninsx of the Counter-Terrorism Committee Executive Directorate (CTED) and Kairat Umarov, Ambassador of Kazakhstan to the UN. Umarov serves as the chairman of the Sanctions Committee on Al-Qaida and Islamic State in Iraq and the Levant, and associated groups.

“Of particular concern is the increasing trend towards attacks carried out by lone terrorists, who are often guided by handlers located in other parts of the world,” Coninsx said.

“Many recent attacks that appear to have been inspired by ISIL, conducted in its name, or claimed by ISIL, were initially reported as ‘lone actor’ attacks. Subsequent investigations have shown however, that those individuals received support or resources from elsewhere, often via the Internet or social media.”

The Islamic State increasingly has become a network of terror cells around the globe, Umarov said. There are currently 256 individuals and 80 entities on the sanctions list.

A report released last month by the Soufan Group, with the Global Strategy Network, evaluates the threat that returning Islamic State jihadists pose to their home countries.

“Although there is disagreement over the threat that returning foreign fighters may present to their countries of residence or origin, or to other countries they pass through,” the report says, “it is inevitable that some will remain committed to the form of violent ‘jihad’ that al-Qaeda and IS have popularized, both within and outside the Muslim world, just as they did following the jihad in Afghanistan.”