According to a United Nations report, almost 25,000 foreign fighters have joined the ranks of militant groups such as Al Qaeda and Islamic State (IS).
Experts said that the flow of foreign fighters is "higher than it has ever been historically," reported the BBC.
While noting that fighters from at least 100 countries had travelled to areas such as Iraq, Syria, Libya and Pakistan, the UN report said that it posed an immediate and long-term threat to global security.
It said that the number of foreign fighters had gone up by about 71 percent between the middle of 2014 and March 2015.
Syria and Iraq have also emerged as a "veritable finishing school for extremists," with some 22,000 foreign fighters.
The report warned that taking on the IS in Iraq and Syria would lead to dispersal of experienced jihadists across the globe.