bauchi nigeria suspect boko haram suicide bombers kill least 13 people attack market northeast nigerian town biu borno state officials say saturday blast strike aid workers distribute food people affect eight-year conflict boko haram say aliyu idrisa community leader addition 13 victims 53 people injure two bombers kill say victor isuku police spokesman borno state saturday attack bore hallmarks boko haram use suicide bombers often women girls attack crowd public space last week suicide bomb mosque northeastern town mubi kill least 50 people one deadly attack recent years government say long-term plan northeast corral civilians inside fortify garrison towns effectively cede countryside boko haram plan string deadly attack raise question assertions nigerian government military boko haram islamist insurgency wipe suspect boko haram suicide bombers kill least 13 nigeria officials