cost of 1,300 american lives. clarissa ward is following this. >> reporter: it is the biggest military victory for isis since last summer when the militant group swept iraq's second largest city of mosul. after four days of intense fighting, iraqi authorities said that 500 people were left dead thousands of civilians fled as the black flag of isis was raised over ramadi. the fall of ramadi came in spite of intensified u.s. efforts to push back islamic state fighters with at least 180 air strikes on the city in the last month. as isis militants flooded in iraqi security forces appeared to flee. policemen abandoned their stations, leaving behind their american-supplied weapons and equipment. ramadi is the largest city in the mainly sunni province of anbar, which stretches from the western edge of baghdad to syria