WASHINGTON - The Justice Department has tapped a veteran prosecutor to probe the flow of foreign fighters including Americans who are joining Syria's rebels, US officials said, in a sign of heightened alarm over the threat of radicalized militants returning home.

US law enforcement and security agencies for months have expressed growing anxiety about a steady stream of Western militants, including Americans, heading to Syria. Most of the foreigners join up with the most extreme factions trying to oust Syrian President Bashar Assad, including Jabhat al-Nusra and the Islamic State of Iraq and the Levant.

US and allied officials say their main fear is that veteran fighters, radicalized by their Syrian experience, will launch terror attacks once they return home. Authorities in Western Europe say they have uncovered plots by fighters returning from Syria.

The Justice Department prosecutor assigned to deal with the issue, Stephen Ponticello, works for the department's national security division.

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