High levels of sectarianism, carnage and the overall grinding nature of Syria’s civil war continue to make that country a top destination for extremists, a top U.S. official said.

“Syria has become the pre-eminent location for al Qaeda-aligned groups to recruit, to train and to equip what is now a growing number of extremists, some of who seek to conduct external attacks,” Matthew Olsen, director of the National Counterterrorism Center, told a congressional hearing on Thursday.

“From a terrorism perspective, the most disturbing element is that al Qaeda has declared Syria its most critical front,” he said. […]