Islamic State militants claimed responsibility on Thursday for a suicide car bombing in a mainly Shi'ite Muslim district of Baghdad that killed at least 20 people the day before.

In a statement posted online, the Sunni militant group said it had targeted a security checkpoint in the al-Shurta al-Rabaa neighbourhood.

The car bomb exploded in a crowded marketplace in a mainly Shi'ite Muslim district of the Iraqi capital on Wednesday.

A further 48 people were wounded by the blast.

A massive blast that killed more than 100 people less than a week ago in the town of Khan Bani Saad was claimed by Islamic State.

Iraqi security forces and Shi'ite paramilitary groups are currently focused on the western province of Anbar, where they have been gearing up for an offensive to retake the mainly Sunni Muslim governorate – Iraq's largest.

The United Nations said earlier this month that nearly 15,000 people had been killed in the 16-month period up to April 30.