Baghdad: At least 21 people died in a dozen blasts and a series of shootings in cities and towns across Iraq on Thursday.
No one has yet claimed responsibility for the latest in a line of attacks since U.S. troops left in December.
Al Qaida's local wing, the Islamic State of Iraq, said it carried out attacks in June and July as part of a renewed offensive.
It has been reinvigorated by the inflow of fighters and cash into neighbouring Syria, providing a morale boost and some extra arms and cash, security experts say. Iraqi insurgents are vowing to retake territory lost during a long war with American troops.
Security has been increased ahead of the end of the Muslim holy fasting month of Ramadan next week, a period when analysts believe insurgents may attempt a major attack.
In Baghdad, a car bomb killed six civilians and wounded 28 in the mainly Shi'ite district of Husainiya on Thursday, police and hospital sources said. Just north of the capital, in Taji, another car bomb injured nine people.
Four car bombs exploded in the city of Kirkuk, 250km north of Baghdad, killing two people and wounded 18, police and hospital sources said.
Kirkuk, which sits on massive oil reserves, is at the heart of a dispute between Baghdad's central government and the country's autonomous Kurdistan region, both of which claim the city as part of their area of territorial control.
Overnight attacks on police checkpoints in the cities of Baquba and Falluja killed six policemen and wounded 13, police and hospital sources said.
There were car bombs, shootings and sticky bombs -- often explosives attached to vehicles with a magnet -- in other towns.
Sunni Muslim insurgents have launched a string of attacks on Shi'ite targets to try to reignite the sectarian violence that killed tens of thousands of people in 2006-2007 and to undermine the country's Shi'ite-led government.
The Islamic State of Iraq insurgents have also said their suicide bombers attacked a counter-terrorism unit in Baghdad in August to try and free prisoners held there.