“The concern is that the al Qaeda networks of the future are being created in this jihadist melting pot,” said Paul Cruickshank, a CNN terrorism analyst who has specialized for years in studying al Qaeda.

An increasing number of them are from Europe — approaching two thousand, according to the ICSR, an unprecedented number, according to experts.

The United States and its allies fear that those fighters will be able to more easily launch attacks in their homelands or against Western targets, said Cruickshank.

“Syria is now the fuel for the jihadist movement and some of the most experienced operatives from Pakistan and Iraq have relocated there,” he said. “Syria has helped al Qaeda rebuild its operations in the Arab world, which has always been its intention anyway.”