A parked car bomb killed 25 people and wounded 115 when it exploded near an intersection in central Baghdad on Thursday and police said the toll was likely to rise as many bodies were still buried under rubble.
Bodies lay strewn around the street after the blast, which smashed three buildings into piles of masonry and concrete. It was at least the fourth to hit the predominantly Shi'ite district of Karrada this week.
US and Iraqi forces have stepped up security operations in Baghdad since mid-February in an attempt to stem bombings, many of them blamed on Sunni Islamist Al -Qaeda, as well as sectarian killings between majority Shi'ites and minority Sunni Arabs.
But large-scale bombings continue to plague the capital.
Residents bundled victims into the boots of cars and the back of pick-up trucks and vans to rush them to hospital as police tried to evacuate stunned residents.
At least one building and several cars were ablaze. Short bursts of gunfire could be heard soon after the explosion.
Karrada, normally one of Baghdad's most stable areas, was hit by three separate blasts on Monday which killed 13 people.
Earlier on Thursday, a parked car bomb killed seven people and wounded 45 near a popular kebab restaurant and shops in the city of Kirkuk, 250 km (155 miles) north of Baghdad.
Separately, the US military said five soldiers had been killed in Iraq over the past two days. Three Marines and a soldier died in combat in volatile Diyala province north of Baghdad on Tuesday.
Another soldier was killed by small arms fire in southern Baghdad on Wednesday.
On Thursday, the US military's second most senior commander in Iraq said militia mortar and rocket crews had been hitting Baghdad's heavily protected Green Zone with greater accuracy in the past three months because of training from Iran.
Lieutenant-General Raymond Odierno's comments came after the U.S. ambassador to Iraq accused Tehran of increasing support for militias when he met his Iranian counterpart for a second round of talks on Iraq's violence on Tuesday.
Iran rejects the allegations.
"In the last three months we have seen a significant improvement in the capability of mortarmen and rocketeers to provide accurate fire into the Green Zone and other places," Odierno, operational commander of USforces in Iraq, said.
"We think this is directly related to training conducted inside Iran," he told a news conference.
Rocket and mortar barrages have hit the sprawling Green Zone, home to the US embassy and Iraqi government buildings, with greater frequency in recent months.
Many of the attacks come from the direction of areas such as Sadr City that have a strong presence of Mehdi Army militiamen loyal to anti-American cleric Moqtada al Sadr.