Islamic State militants have claimed responsibility for an overnight suicide bombing in the Iraqi capital Baghdad killing at least 23 people.

The hardline Sunni Islamist group, which has led an offensive through northern and western Iraq, said the explosion in Kadhimiya, site of a major Shia shrine, was carried out by one of its fighters.

Officials initially put the death toll from the bomb at 23, but hospital and morgue officials said this morning it had risen to 33.

The Islamic State has claimed responsibility for a wave of bombings in Baghdad, including several blasts on Saturday, which killed 27 people.

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 100km from the capital.

Government forces launched a counter-offensive a week ago to recapture Tikrit, home city of executed former president Saddam Hussein.

However, they withdrew within hours after coming under fierce onslaught from the militants.

This morning an air strike by government forces on a civilian neighbourhood in the town of Sharqat, north of Tikrit, killed 12 people, a hospital source said.

Security forces also found the bodies of eight Iraqi soldiers 3km outside Samarra, the most northern city under full government control.

The UN envoy in Iraq, Nickolay Mladenov, has called on the UN Security Council to firmly demand an end to the atrocities.

Mr Mladenov told the 15-member Council that it was time to take a stand to end to the violence, enforce sanctions to isolate the Islamic State, and bring perpetrators of war crimes to justice.

"Recruiting and using foreign fighters, engaging in murder, hostage-taking, kidnappings, gross human rights violations, all of which are reasons why the international community and the Security Council should demand, in no uncertain terms, that IS cease all hostilities and atrocities," he said.

The top world body must "call upon member states to cooperate in efforts to enforce existing sanctions and hold accountable the perpetrators, organizers and sponsors of these horrific terrorist acts, war crimes and crimes against humanity," Mr Mladenov said by video conference from Baghdad.

The UN Security Council has denounced the persecution of Christians and urged Iraqi politicians to come together to fight the al-Qaeda offshoot that now controls one third of Iraq including Mosul, the country's second city.

IS is on the UN list of terror groups as an al-Qaeda affiliate and is the target of international sanctions.