According to a U.N. report, an estimated 15,000 fighters from around the world have left their homes to join extremist groups operating in Iraq and Syria. It adds that actual numbers could be even higher.
The report, which was submitted to the U.N. Security Council by a panel that monitors al Qaeda and the Taliban, states that foreign fighters are joining the Islamic State and other extremist groups on "an unprecedented scale." They are coming mainly from the Middle East, Western Europe and North Africa, although there are also some Asians and a smaller number of Americans.
The report warns that if radicalization of foreign fighters continues when they return to their homes or even third states, the threat of extremist violence "could swiftly increase in areas as diverse as Europe, the Maghreb, Asia and Africa."
The numbers of fighters are now many times the numbers of all foreign extremist fighters from the previous decade, and growing, the U.N. says.
Nationals or residents from more than 80 countries have joined these extremist groups. The report does not list the specific countries.
The U.N. states that in 2014, the foreign fighters included networks of ethnic Chechens — as well as individuals from France, Russia, Britain and Northern Ireland operating together.
Many of the senior commanders of al Qaeda and the Islamic State are now veterans of other conflicts — bringing a range of skills, capabilities and social networks "that enhance the terrorist threat," the report says.
The United Nations in September adopted a resolution compelling countries to work to prevent their citizens from traveling to join terrorist organizations.