(Updates with more detail, background) By Ross Colvin BAGHDAD, Oct 11 (Reuters) - Militiamen firing mortars detonated a U.S. ammunition dump in Baghdad on Tuesday night, sparking a barrage of explosions that continued to shake the capital on Wednesday morning, a U.S. military spokesman said. Residents said the blasts were reminiscent of the aerial bombardment of Baghdad that preceded the U.S. invasion of Iraq in 2003. A mortar round fired from the Abu Dsheer area of southern Baghdad caused the fire in an ammunition holding area in Camp Falcon, a forward operating base for U.S. troops, that ignited tank, artillery and small-arms ammunition, the spokesman said. "Intelligence indicates that civilians aligned with a militia organisation were responsible for last night's mortar attack," said Lieutenant Colonel Jonathan Withington, spokesman for the U.S. 4th Infantry Division. Withington said there were no reports of casualties among soldiers on the base or Iraqi civilians in neighbouring districts. He did not identify the militia organisation but residents of Abu Dsheer, a mostly Shi'ite area in the Sunni district of Doura, told Reuters the Mehdi Army militia of radical Shi'ite cleric Moqtada al-Sadr was a growing presence in the area. The Islamic Army in Iraq, one of a number of militant groups operating in the country, had earlier claimed responsibility for the attack in a Web site posting. The fire, which erupted at about 10.40 p.m. (1940 GMT), sent flames and showers of sparks into the night sky and triggered dozens of explosions that shook buildings several kilometres away in central Baghdad. "The fire is still smouldering and rounds are continuing to cook off," Withington said. Three battalions are based at Camp Falcon, along with Abrams main battle tanks, Bradley fighting vehicles and Strykers. The troops are part of Operation Together Forward, a major operation to quell violence in Baghdad in which U.S. and Iraqi troops have been sweeping through selected city districts to root out insurgents and sectarian death squads. They have yet to enter the sprawling slum of Sadr City, the main stronghold of the thousands-strong Mehdi Army. Prime Minister Nuri al-Maliki has vowed to disband all militias, including those linked to parties within his own government. The Mehdi Army, under Sadr's leadership, launched two uprisings against U.S. forces in 2004, but the cleric has since embraced politics, joining Maliki's four-month-old government. Nevertheless, his militia remains a powerful force and has increasingly clashed with U.S. and Iraqi forces in recent weeks. At least 20 Iraqi soldiers were killed in a battle with Mehdi Army militiamen in the southern city of Diwaniya in August, and at the weekend, the U.S. military said 30 militiamen were killed in a battle with U.S. and Iraqi troops in the city.
