A car bomb exploded on Wednesday in a crowd of day labourers waiting for jobs in central Baghdad, killing eight people and wounding 28, police said.
Five other people were killed in a gunfight in the northern city of Mosul. The blast occurred at about 11:10 am in the Nahda district, police Lt Bilal Ali said.
He said all the dead were civilians but four policemen were among the wounded.
In Mosul, 360 kms northwest of Baghdad, armed clashes erupted on Wednesday between police and assailants in three neighborhoods on the western side of the Tigris River, police Lt Col Abdul-Karim Ahmed Khalaf said.
At least five gunmen were killed and six were arrested, he said. Western Mosul is predominantly Sunni Arab, while Kurds dominate in the east of the city.
The clashes occurred one day after a suicide car bomber killed nine people in an attack on the Mosul headquarters of the Patriotic Union of Kurdistan, a Kurdish party headed by President Jalal Talabani.
Elsewhere, the Iraqi army general command said Wednesday that order had been restored in the Shiite holy city of Karbala following street battles the day before between security forces and followers of anti-American cleric Mahmoud al-Hassani, which left 12 dead, including two Iraqi soldiers.
The clashes erupted after police raided the cleric's office, ostensibly looking for weapons. Gangs of al-Hassani's followers roamed the streets on Tuesday, firing Kalashnikovs, machine guns and rocket propelled grenades at police and army patrols.
Security forces rounded up 281 people in the wake of the clashes, the army statement said.
Al-Hassani gained prominence for his nationalistic stand, calling for an Iraq free of influence from the Americans and Shiite-dominated Iran.
Other key Shiite figures have sought to dampen his influence, which is mostly in Karbala and Basra, Iraq's second-largest city.
In Baghdad, meanwhile, assailants blew up a monument erected to 18 Shiite children who were killed in July 2005 suicide bombing in the city. One American soldier was also killed as he was distributing candy to the children.
Sectarian unrest in the Baghdad area has prompted the US command to order 12,000 US and Iraqi reinforcements into the streets of the capital.
US Ambassador Zalmay Khalilzad has described sectarian violence in Baghdad as the greatest threat to Iraq's future.
However, many other parts of the country remain unstable after three years of the US-led international military presence, including the Sunni insurgent stronghold of Anbar and Basra, where British forces have failed to prevent Shiite militias from infiltrating the police and security services.