At least 15 people were killed in a twin suicide bombing on a Shiite mosque in Baghdad on Thursday, police and medical sources said.A further 50 people were wounded in the blast in the predominantly Shi'ite Shulaa neighbourhood of the Iraqi capital.The first assailant detonated his vest inside the mosque and the second blew himself up when security forces gathered at the site of the initial blast.Four of the victims were members of the security forces, the sources said.There was no immediate claim of responsibility for the blast but Shi'ite Muslims in Iraq are often targeted by Daesh militants.