SAMAWA, Iraq, Oct 5 (Reuters) - Gunmen stormed a home in the southern Iraqi city of Samawa late on Wednesday, shooting dead three women and slitting the throat of a baby girl, neighbours and hospital officials said on Thursday. Neighbours said the women were a mother and her daughter-in laws. The 18-month-old infant was the daughter of one of the in-laws. The women, all Shi'ites, the neighbours said, were killed in an overwhelmingly Shi'ite city. Violence there is almost non-existent, but revenge killings are fairly common in Iraq's south.