Authorities intercepted them in Germany, then returned them to their families without criminal charges.

That case and others like it show how the militant group is targeting its sophisticated propaganda beyond male fighters, seeking to entice not only wives but also professionals such as doctors, accountants and engineers as it pushes to build a new society in a territorial base that has spread across broad swaths of Iraq and Syria.

The motives of this diverse pool of recruits perplex Western governments trying to stem the flow. One recruit, Shannon Conley, a Colorado woman who was caught and is being sentenced next month, sought to fight in Syria or use her nursing skills to help fighters there.

The group "is issuing a bit of a siren song through social media, trying to attract people to their so-called caliphate," FBI Director James Comey told reporters.

"And among the people they're trying to attract are young women to be brides for these jihadis."

As IS seeks to expand its footprint, it conscripts children for battle, recruits Westerners for acts of jihad and releases videotaped beheadings that shock in their exposure of the group's violent intentions.

But the organization also uses propaganda with a humanitarian appeal, such as photos of bombed-out Syrian villages coupled with pleas for help.

Images in videos of smiling children being given treats and enjoying stuffed animals paint a family-friendly portrait that suggests roles within the proto-state for wives and mothers.

Even as they preach violence, "they'll do the warm and fuzzy ... the gun in one hand and the kitten in the other," Assistant Attorney General John Carlin, head of the Justice Department's national security division, said in an interview.

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