A fuel tanker explosion has killed at least 10 people and wounded 15 at a busy crossroads in Baghdad.
Several vehicles caught fire after the tanker exploded
The blast happened on a crowded road in Baghdad's western district of Bayaa and enveloped other vehicles in flames.
Police said a collision with a bus had set off a bomb in the tanker as it was heading for a local police station.
But a US military official said it was a traffic accident and explosive experts had examined the scene, finding no evidence of explosives.
Bombers attacked two police stations in the Baghdad area on Monday, killing nine people.
Attacks on the US-led coalition and its Iraqi allies have not eased since the capture of the former Iraqi president near Tikrit - which was hailed by the coalition as a psychological turning point.
US troops have also been rounding up scores of suspects after an ambush in the town of Samarra as pro-Saddam rallies continue in the Sunni Muslim heartland, where loyalty to the ousted regime was strongest.
Car crash theory
The BBC's James Rodgers reports that Wednesday's tanker blast was heard across the Iraqi capital.
MAJOR ATTACKS SINCE 1 MAY
14 December: Car bomb at police station kills 17 in Khalidiya, west of Baghdad
12 November: 26 die in suicide attack on Italian police base in Nasiriya
2 November: 16 US soldiers die as Chinook helicopter downed
27 Oct: Red Cross and other buildings in Baghdad bombed, more than 30 killed
29 Aug: Mosque near Najaf bombed, at least 80 dead including Shia Islam's top cleric in Iraq
19 Aug: UN headquarters in Baghdad bombed, 23 killed including head of mission
List covers attacks since US declared war effectively over
Witnesses at the scene of Wednesday's blast told French news agency AFP it had spread devastation across a wide crossroads, incinerating people in their cars.
"There were lots of human remains on the sidewalks and we started collecting them," said Ahmed Ayyoub, a bus driver.
Hassan Haidar Khattab, another witness, said the tanker had appeared to be following a US military convoy when it was struck by a passenger car.
Other eyewitnesses said the tanker was being pursued by police who fired on it, causing it to explode.
"What can we do?" one victim told Reuters news agency as he lay in his hospital bed.
"It's our future. Our future is death."
US forces have now arrested nearly 80 suspected militants in Samarra, north of Baghdad, where a convoy was ambushed on Monday.
Backed by attack helicopters and armoured cars, they launched new raids on Wednesday, picking up eight fresh suspects to add to 70 arrested earlier.
Samarra was scene of a bloody battle with US troops in late November
The soldiers forced their way into houses in the middle of the night, blowing down gates with plastic explosives, the French news agency AFP reports.
Lieutenant Jack Saville of the 4th Infantry Division told the agency that the troops were hunting for militants or their backers based on information from local residents or Iraqi contractors working on a US army base.
An army statement said the raids were intended to "target, isolate and eliminate former regime elements and other anti-coalition cells that continue to try to destabilise Iraq and intimidate innocent Iraqi citizens who choose freedom over tyranny".
The US army suffered no casualties in Monday's ambush but reported killing 11 militants.
Local people disputed the US version, saying only one man, a labourer, had been killed and that troops had sprayed the town with indiscriminate fire.