Seven car bombs exploded across Baghdad on Monday, killing at least 37 people and wounding scores, in what U.S. and Iraqi officials said was a co-ordinated strike by al Qaeda militants.
One of the bombs exploded at a popular market in the Shi'ite Muslim slum of Sadr City in east Baghdad killed at least 12 people.
Another car bomb blew up next to a group of labourers queuing for work, killing six people. Hours later, south Baghdad's Um al-Maalif neighbourhood was shaken by two blasts in a market, killing 12.
The latest attacks underscore the challenges Iraqi security forces face as U.S. troops prepare to leave by the end of 2011.
Overall violence has fallen in Iraq to levels not seen since just after the 2003 U.S. invasion, but militants, especially Sunni Islamist al Qaeda, still carry out large-scale bombings.
Iraqi Prime Minister Nuri al-Maliki said the attacks were a "gift" from members of Saddam Hussein's once omnipotent Baath party, aided by al Qaeda. The 62nd anniversary of the pan-Arab nationalist party's foundation in Syria falls on Tuesday.
"The seven car explosions are a gift from the buried Baath party in memory of its foundation, which was an evil omen for the Iraqi nation," he said in a statement.
A separate statement from Iraq's Presidency Council, headed by President Jalal Talabani, expressed deep concern about the blasts and called for action from the security forces.