In response to the killing of the four US citizens, and intense political pressure, the US Marines commenced Operation Vigilant Resolve. They surrounded the city and attempted to capture the individuals responsible as well as others in the region who might have been involved in insurgencies. One out of every two mosques in Fallujah were used to hide fighters or weapons. The Iraqi National Guard was supposed to work alongside the US Marines in the operation, but on the dawn of the invasion they discarded their uniforms and deserted. Under pressure from the Iraqi Governing Council, the US aborted its attempt to regain control of Fallujah. The US Marines suffered 40 deaths in the siege. Estimates of the number of Iraqi deaths (both fighters and civilians) in the attack range from 271 (according to Iraqi Ministry of Health officials) to 731 (according to Rafie al-Issawi, the head of the local hospital).