Mortar rounds crashed down on a market place in a neighbourhood of southwest Baghdad on Friday killing 12 people and wounding 40, a medical source said. First one round struck the Umm al-Maarif neighbourhood, attracting a large crowd of worried onlookers, then three more slammed into them, killing a dozen people, including children, the doctor at the capitalÂ’s Yarmuk hospital said. Separately, tribal commander said his fighters had joined nationalist insurgents fighting Al Qaeda in Baghdad street battles. An Iraqi cameraman working for AP was shot and killed in Baghdad on Thursday, the US news organisation said.