Nineteen people were killed and 56 others wounded when a car bomb ripped through a busy market in southern Iraq on Wednesday, a local official said.
"The final toll is 19 dead and 56 injured," said Mohaned Abdul Redha, the hospital's chief of emergency services.
The death toll from the explosion in the town of al-Bathaa, 30 km (20 miles) west of Nassariya, could rise, said Akram al-Tamimi, media manager of the provincial council of Nassariya.
Batha's police chief was fired in the aftermath of the attack, and an inquiry has been launched to determine whether police could have prevented the bombing.
The number of casualties was the highest in a single attack since May 20, when a powerful car bomb tore through a Baghdad street full of diners, killing 34 people and wounding 72.
Batha town mayor Ali Fahad said "children and women" were among the dead.
The bombing followed an attack on Tuesday that killed two anti-Qaeda militiamen and wounded their commander in the town of Tarmiyah, north of Baghdad.
In another attack in the center of the former rebel bastion of Fallujah west of Baghdad, five civilians were wounded when a bomb fixed to a parked motorcycle exploded.
Seven people were also killed and dozens wounded in Baghdad on Monday when a sticky bomb planted on a minibus exploded, security officials said.
That attack occurred in the mixed southern district of Dora, which has been hit by a number of attacks in recent weeks.
May saw the fewest Iraqi deaths from violence since the U.S.-led invasion of 2003, with 124 civilians, six soldiers and 25 policemen killed in attacks, according to official figures.
Despite a surge in violence in April, Iraq has insisted that the U.S. pullout timetable, enshrined in a landmark security pact concluded with Washington in November last year, will not be altered.
The U.S. military is scheduled to leave major urban areas by the end of this month in a key step ahead of a complete withdrawal by the end of 2011.
Recent attacks in Baghdad have mainly targeted Iraq's majority Shiite community, prompting speculation about a return of al-Qaeda-style attacks aimed at reigniting the sectarianism that swept the country two years ago.
April saw a string of deadly bombings in Shiite and mixed neighborhoods of Baghdad that were reminiscent of attacks that occurred at the height of Iraq's sectarian fighting in 2006.
At that time such bombings triggered reprisal attacks in which thousands of mostly Sunni men were abducted, tortured and executed, but the recent wave of bombings has not sparked sectarian fighting.
Though Nasiriyah was one of the sites of an Iraqi army offensive against Shiite gunmen last year, the city and its surroundings have rarely been hit by bombings.