A new United Nations report says that more than 25,000 fighters have left their homes bound for Iraq, Syria and other countries to join terrorist networks such as the self-proclaimed Islamic State and the al-Qaida-linked al-Nusra Front.
The report says the fighters hail from more than 100 countries worldwide, according to The Associated Press.
Syria and Iraq are the prime destinations, where jihadists can live and work in what the U.N. called an "international finishing school" for extremists, much as Afghanistan was during the 1990s.
The U.N. report was written by a panel of experts tasked with monitoring violations of sanctions against al-Qaida. The U.N. Security Council asked the experts six months ago to investigate the threat from foreign fighters joining the Islamic State and other militant groups.
In the report filed to the council late last month, the experts say the flow of foreign fighters has risen from a few thousand a decade ago and is now "higher than it has ever been historically." In just the past year, the number of foreign fighters worldwide has jumped more than 70 percent, according to Reuters.
The news service says more than 20,000 foreign fighters traveled to Syria and Iraq, while 6,500 are in Afghanistan and hundreds in Yemen, Libya, Pakistan and Somalia.
The U.N. report highlighted the effect of social media networks that had linked "diverse foreign fighters from different communities across the globe," and noted that the chances of foreign travelers becoming caught up in terrorist incidents was "growing, particularly with attacks targeting hotels, public spaces and venues", according to the BBC.
The Security Council adopted a resolution in September demanding that all states make it a serious criminal offense for their citizens to travel abroad to fight with militants, or to recruit and fund others to do so, the BBC says.
The report called for greater intelligence sharing among nations to help identify foreign fighters. It also noted that if the Islamic State were defeated in Syria and Iraq, the foreign fighters could be scattered across the world.