Reuters reports Islamic State militants claimed responsibility on Wednesday for an overnight suicide bombing in a Shi'ite district of Baghdad which killed 33 people, one of the deadliest recent attacks in the Iraqi capital. The hardline Sunni Islamist group which has led an offensive through northern and western Iraq said the explosion in Kadhimiya, site of a major Sh'ite shrine, was carried out by a fighter it named as Abu Abdul-Rahman al-Tunisi (the Tunisian). Officials initially put the death toll from the bomb at 23, but hospital and morgue officials said on Wednesday morning it had risen to 33, with more than 50 wounded. Sunni fighters led by the Islamic State swept through most of Iraq's Sunni Muslim provinces towards Baghdad last month, their advance halted less than 100 km from the capital. Government forces launched a counter-offensive a week ago to recapture Tikrit, home city of executed former president Saddam Hussein, but withdrew within hours after coming under fierce onslaught from the militants.