Foreign fighters continue to flow into Syria to join the "Islamic State of Iraq and Syria" (ISIS), but at a much slower rate, US Chairman of the Joint Chiefs of Staff General Joseph Dunford said Tuesday (October 16th).

New followers arrive at a rate of about 100 a month, he said, down from a peak of about 1,500 a month three years ago, AFP reported.

However, this shows that ISIS’s ability to attract followers remains potent, Dunford said.

"It is the flow of foreign fighters, the ability to move resources, and the ideology that allows these groups to operate," Dunford said, opening a conference on countering violent extremism.

Dunford also said the inflow adds to the mounting problem of how to handle hundreds of captured foreign fighters whose home countries will not take them back.

He said the Syrian Democratic Forces (SDF) are holding more than 700 ISIS fighters from around 40 countries.

"The progress of returning these fighters home for prosecution has been delayed by political considerations and inconsistent legal frameworks," he said.

Dunford said not dealing with the captured foreign fighters correctly will make it harder to eventually extinguish the attraction of the ISIS ideology.

A critical factor, he said, "is how we identify, prosecute, deradicalize and reintegrate foreign fighters".

"We need to find a way to address this challenge and prevent the detainees from becoming the leaders of tomorrow's extremist organisations," Dunford said.