Sheehan noted that immigrant and minority communities in the United Kingdom were more isolated, compared to those in the United States. That isolation could make UK-born, second-generation citizens more susceptible to al Qaeda recruiting.
The U.S. has an incredible capacity to accept minorities . . . [and] they are very well assimilated," he said. "In the U.K., they had more ghettoized immigrant communities, and we talked to them extensively about that issue."
Al Qaeda's cell in Yemen, dubbed al Qaeda in the Arabian Peninsula (AQAP), has pressed particularly hard to reconstitute its ranks with Western recruits.
Recent AQAP postings on various radical Islamist websites call for Western volunteers to carry out future attacks the United State, Israel and Western Europe.
Aside from the United States, AQAP recruiters have also listed possible strikes in France, Britain and other "apostate" governments around the world as top priorities for incoming operatives.
In March, 30-year-old Army veteran Eric Harroun, was charged with conspiring with a known terrorist organization after allegedly fighting alongside al Qaeda factions in Syria.
Harroun also faces federal charges for use of a "weapon of mass destruction" when he was trained to use rocket-propelled grenades (RPGs) by members of the Al-Nusra Front.
Al-Nusra Front, also known as Jahbat al Nusra (JAN), is the al Qaeda-affiliated Islamic militant group whose forces have been on the front lines alongside anti-Assad rebels throughout the two-year Syrian civil war.