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 .
Militant group Ansaru says 7 foreign workers are dead . Ansaru is believed to be an offshoot of Boko Haram , U.S. officials say . The victims are from Italy , Greece , Lebanon and Britain . The foreigners worked for a construction firm in northern Nigeria .