Over 60 people were killed on Sunday in bomb explosions in Baghdad and the northern oil centre of Kirkuk, police said.
The incident dramatically escalated tension as Iraqi Prime Minister Nouri Al-Maliki left for Washington for talks on reversing the latter's slide towards civil war.
The blast occurred when a suicide driver detonated a minivan in the Mahdi Army stronghold of Sadr City at the entrance to the Jameelah market.
An Iraqi army statement said that 34 people were killed and 73 were wounded.
Eight more were killed and 20 were wounded when a second bomb exploded two hours later at a municipal government building in Sadr City, the Iraqi army said.