At least 20 people were killed and 50 injured Thursday when two women suicide bombers in Iraq attacked pilgrims in Iskandariyah district 40 kilometres south of the capital, sources said, according to dpa. The female bombers were wearing explosive belts and blew themselves up amid a group of Shiite pilgrims on their way to the holy southern city of Karbala to commemorate the birth of the 12th Imam revered by Shiites. US and Iraqi authorities say al-Qaeda militants have increasingly relied on women to conduct suicide attacks, as they can evade security searches. A report released in June by the Baghdad-based Monitor of Constitutional Freedom and Bill of Rights said an increase in women suicide bombers is due to dire economic conditions and a culture of sectarianism and marginalization. In July, three suicide attacks carried out in quick successionon against Shiite pilgrims in Baghdad left at least 25 people dead and 40 injured. Three women wearing explosive belts struck convoys of pilgrims on their way to a Shiite shrine in Kadimiya in north-western Baghdad to mark the death of a revered 8th-century imam, Musa al-Kazim. Extremist Sunni Muslim groups, mainly al-Qaeda in Iraq, have often targeted Shiite pilgrims during annual celebrations of religious events. Those groups consider Shiite Islam a heresy. Earlier on Thursday, an explosive device in Baghdad killed two police officers and injured five people, including three police officers and two civilians in an attack on a police patrol. Meanwhile, a blast in centre Baghdad in the Tahariyat square in al-Karada district killed two civilians and injured five people. The explosion also destroyed three vehicles, a police source told Voices of Iraq (VOI) news agency. In restive Diyala province, a bomb targeting a police patrol killed two policemen and injured six people, a security source said. The bomb struck a police patrol in Baquba, the capital of Diyala, located some 60 kilometres north of Baghdad. In two other separate incidents, unidentified gunmen killed an Iraqi policeman and a soldier during their vacation in the northern city of Mosul, a police source told VOI. In a parallel incident, gunmen opened fire on an Iraqi soldier and his companion as he was also on vacation. The soldier was shot dead and his companion was injured. The shooting took place in Seha neighbourhood in western Mosul, the source added. Mosul is located some 405 kilometres north of Baghdad.