An Iraqi Interior Ministry official says 13 people are in custody in connection to last week's coordinated bombings in Baghdad that killed 127 people and wounded 400.
Sunday's announcement of the arrests came as lawmakers again questioned officials about security lapses in the capital, where there have been three massive attacks since the beginning of August.
An al-Qaida-linked group known as the Islamic State of Iraq has claimed responsibility for Tuesday's bombings and warned of more attacks.
On Saturday, Iraq's Interior Minister Jawad al-Bolani said security forces had prior warning of Tuesday's bombings. He said bureaucracy and a lack of cooperation between government ministries were to blame for security gaps and the inability to stop the attacks.
In violence Sunday, Iraqi police say three car bombings in other parts of the country killed at least three people and wounded more than 30 others.
Officials said one car bomb exploded near Fallujah, killing two people and wounding at least seven. Police say the bomb appeared to target a senior security officer, Colonel Saad al-Shimari, who escaped unharmed. At least one child was among the victims in the attack.
Another car bomb blast in Fallujah Sunday wounded at least five people near the home of an official.
In the northern city of Mosul, a car bomb exploded near a group of Iraqi army recruits, killing one person and wounding 19 others.
Violence in Iraq has declined in recent months, but militants have continued sporadic attacks. The assaults usually target security forces but frequently harm civilians.
Some information for this report was provided by AP, AFP and Reuters.