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Ms. Speier cautioned that little is known about Boko Haram in part because of its “rapid rise.” She urged U.S. agencies to redouble their efforts to find out about its “membership strength and leadership cadre,” as well as “the true nature of its ties to other groups.”

She called for increased counter-terrorism cooperation with the Nigerian government and “outreach to the Nigerian people, especially the Muslim community,” to help U.S. officials “better understand the appeal of a group like Boko Haram.”

About half of Nigeria’s 155 million people are Muslims and 40 percent of the population is under 40 years old.