The blast took place shortly before 9 a.m. near a central thoroughfare in Fallujah, 40 miles (65 kilometers) west of Baghdad. The city was once at the heart of the Sunni insurgency in the western Anbar province until tribal leaders turned against al-Qaida in Iraq, a turning point of the war.
The street was crowded with pedestrians, stalls selling tea and day laborers gathering for work when the blast occurred, a Fallujah police officer said. He spoke on condition of anonymity because he was not authorized to talk to the media. Blood pooled around charred and mangled wrecks of several cars destroyed by the blast.
Partial election results from Anbar showed a secular bloc led by former Prime Minister Ayad Allawi in the lead, winning nearly 100,000 votes more than his closest competitor, the Sunni coalition Iraqi Accordance.
Allawi, a Shiite who has emerged as the main rival to Prime Minister Nouri al-Maliki in the vote, has been drawing on heavy Sunni support in his campaign, attracting Sunni voters frustrated with their own leaders who are also attracted to Allawi's nonsectarian stance and anti-Iran rhetoric.
Iraq's electoral commission was expected to release updated preliminary results from the voting in all 18 provinces later Monday, based on 60 percent of the returns. However, more delays were possible in the slow counting process that has been plagued by confusion and disarray.
Nobody claimed responsibility for Monday's attack but it bore the hallmarks of al-Qaida in Iraq, which has threatened an uptick of violence in connection with the elections.
Political parties are already jockeying for power and poised to negotiate new alliances to form the next government, which will lead the country as U.S. forces begin withdrawing ahead of a 2012 deadline.
Results released so far show al-Maliki's State of Law bloc ahead in seven provinces, boosting his chances of retaining the prime minister's post although he was unlikely to win the majority necessary to govern alone.
Allawi's Iraqiya list had the lead in five provinces, while the religious Shiite Iraqi National Alliance and the main Kurdish coalition each were winning in three, according to partial results.
The narrow race was likely to mean months of political wrangling as leaders try to cobble together a coalition government.
The March 7 vote was Iraq's second for a full-term parliament since the U.S.-led invasion in 2003.