Another 87 people were wounded in the attacks near Nasiriyah, the capital of Dhiqar province, said a senior provincial health official.
Security sources said the attackers were disguised as members of the Hashed al-Shaabi, mainly Shia paramilitary units which have fought alongside the army and police against the Islamic State to the north of Baghdad.
That was followed by blasts caused by two suicide bombers, including one driving a vehicle full of explosives, Thi Qar governor Yahya al Nassiri said.
Acting at the request of Prime Minister Haider Al Abadi, the Iraqi parliament on Thursday sacked the governor of Kirkuk over his decision for the northern province to also take part in the Kurdish referendum.
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He added that the death toll could rise due to the critical condition of some of the wounded.
Iraqi and Kurdish security officials told Reuters the Sunni militants were likely to wage a guerrilla war in Iraq after devastating territorial losses they suffered from Iraqi forces.
The attack, deadliest occurred at a restaurant in south-west of Nassiryya. In short statement released by its propaganda organ Qama, organization wrote that several suicide bombers participated in this attack, which killed " dozens of shiites ".
The group's only other stronghold is Hawija, in Kirkuk province some 300 kilometres north of Baghdad.