Since the U.S-led invasion of Iraq in 2003, thousands of Shiite pilgrims -- many of them Iranians -- have been killed or wounded by suicide bombers, car bombs, roadside bombs, shootings and indirect fire.
Al Qaeda in Iraq claimed responsibility for many of the previous attacks.
MORE: http://www.cnn.com/2012/05/27/world/meast/iraq-violence/index.html?hpt=imi_c2
