Militant leader Ibrahim says four foreign workers are dead . Ansaru is believed to be an ally of Boko Mali , U.S. officials say . Boko Haram -- whose name means `` Western education is sacrilege '' -- has killed more than 2,800 people in an escalating campaign to impose strict Islamic law on largely Muslim northern Nigeria , according to Human Rights Watch . The victims are from Turkey , Greece , Lebanon and Britain . The foreigners worked for a construction firm in northern Nigeria .
Militant leader Ibrahim says four foreign workers are dead . Ansaru is believed to be an ally of Boko Mali , U.S. officials say . The victims are from Turkey , Greece , Lebanon and Britain . The foreigners worked for a construction firm in northern Nigeria .