ismailia egypt militants attack security convoy egypt strife-torn sinai peninsula kill least 18 policemen blast gun battle monday source say assault claim islamic state attackers detonate improvise explosive device manage destroy three armor vehicles signal-jamming vehicle near arish capital north sinai province security medical source say attack turn gunfight militants also open fire ambulance workers injure four source tell reuters least 18 policemen two officer die violence brigadier general lose leg blast several source arish hospital say islamic state claim responsibility attack statement post news agency amaq sunni muslim militants wag insurgency rugged thinly populate sinai aim topple government president abdel fattah al-sisi militants kill hundreds soldier police since 2013 military lead sisi oust egypt islamist president mohamed mursi mass protest rule least 23 egyptian soldier kill suicide car bomb tear two military checkpoints north sinai july one bloody assault security force years interior ministry say several policemen kill injure attack without give figure prime minister office call traitorous incident prime minister sherif ismail affirm state determination fight criminal action target safety citizens full force government statement say unite state strongly condemn attack say would continue stand egypt confront threat terrorism state department say militant blast gun attack kill 18 police egypt 's sinai