AFP, Washington :The United States believes it has killed about 6,000 jihadists in its air strikes against the Islamic State group, defense officials said Thursday.Pentagon chief Chuck Hagel, however, warned against resorting to “body counts” to measure progress in the war.The estimate of how many IS fighters had been taken out by US-led air raids was first cited by Washington’s ambassador to Iraq, Stuart Jones in an interview aired Thursday by Al-Arabia television.US defense officials reluctantly confirmed the figure but insisted the military was not placing a priority on the measurement, which carried uncomfortable echoes from the Vietnam conflict-when American commanders cited daily “body counts” to convey progress in the war.There was no independent confirmation of the casualty estimate and it remains unclear how many civilians might have been inadvertently killed in the strikes.