Secretary-General Antonio Guterres said Monday that reports suggest there has been "a surge in the use of mercenaries," who are not only fighting in wars and illegally exploiting natural resources but are now "feeding off" transnational organized crime, terrorism and violent extremism.

The U.N. chief called for much broader support for regional and international conventions against the use of mercenaries and said those compacts need to be updated. He also called for prosecuting mercenaries and for strengthening efforts at preventing people, especially the young, from being recruited as mercenaries.

Guterres told the Security Council that while "the shadowy nature" of mercenaries makes data hard to come by, their impact is clear in the worsening of conflicts, weakened stability of countries, the undermining of the rule of law and the large numbers of people forced to flee their homes.

Read more: Minneapolis Star-Tribune