Although they encountered great difficulties against the evasive guerrilla bands, the majority of the insurgents in the city had been killed or captured by late November. Significant guerrilla resistance, however, continued until January (much of it by insurgents operating out of pre-prepared hidden tunnels). By the end of most of the fighting, over 50 U.S. Marines had been killed and several hundred wounded. As many as 3,000–4,000 insurgents may have been killed, according to U.S. military estimates. Reports suggested a heavy toll among remaining civilians in the city as well. Most of the city suffered severe damage from the fighting by the battle's end. In the months to come, only a small fraction of refugees from the city would permanently return. The attack on Fallujah had unintended consequences for much of the rest of Iraq. Insurgents fleeing Fallujah filtered into northern Babil province, Mosul in the north, and Baghdad itself. As a result, a sharp spike of violence was seen upon the attack's commencement, with mortar and IED attacks increasing in frequency and intensity. The campaign of suicide bombings and car bombings, mainly affecting Iraqi civilians, intensified to the worst point ever seen. The worst violence was seen in Mosul. Insurgents launched a massive offensive, seizing the western (Arab) half of the city and effectively destroying the police force at the same time the U.S. launched its assault on Fallujah. On November 16, over 3,000 U.S. troops and a similar number of Iraqi troops launched a counteroffensive, dismantling insurgents from strategic points but failing to break their hold on most of the city. Mosul, which a year earlier was relatively peaceful compared to much of Iraq, would be a scene of some of the heaviest sustained fighting for some time to come. In December, 14 American soldiers were killed and over a hundred injured when an explosion struck an open-tent mess hall in Mosul, where President Bush had displayed a Thanksgiving turkey the year before. It was one of the most costly attacks on U.S. troops during the war – the explosion is believed to have come from a suicide bomber. With the year's end, the U.S. military reported that they had killed or captured at least 15,000 guerrillas over the course of 2004, giving a new perspective on the intensity of the fighting during that period. 848 U.S. soldiers were killed in 2004, and 9,034 were wounded in action.