At least 76 people have been killed in four bomb attacks in market areas of the Iraqi capital Baghdad.
The blasts in Shorja also caused heavy damage to buildings
Three explosions in quick succession at the Shorja market killed at least 71 people and wounded about 164.
Half an hour earlier a parcel bomb exploded at the Bab al-Sharqi market, killing five people, police said.
The blasts came either side of a 15-minute pause to commemorate the sectarian bombing of an important Shia Muslim shrine in Samarra one year ago.
The Samarra attack - on 22 February 2006, but a year ago by the Islamic calendar - triggered an upsurge in sectarian violence which still grips the country, costing thousands of lives a month.
An interior ministry spokesman later said three people, including two foreigners, were arrested in the hours after the blast.
Brig Gen Abdel Karim Khalaf said the bombs were planted by a new cell, and were booby trap devices instead of suicide attacks, the Associated Press reported.
Shorja market was once Baghdad's main shopping area, but amid the violent division of Iraq's religious communities it is now mostly a Shia Muslim area, and a target for Sunni extremist groups.
Bab al-Sharqi is a rarer phenomenon in Baghdad, correspondents say, in that it is still frequented by Sunni and Shia traders and customers.
The Shorja blast almost coincided with the end of a quarter of an hour's pause starting at midday (0900 GMT), when Iraqis had been urged by Prime Minister Nouri Maliki to stop work to mark the Samarra attack.
Mr Maliki at the same time ordered thousands of extra security forces onto the streets as part of a much-heralded joint Iraqi and US security plan.
One report said two cars packed with explosives were detonated in quick succession at Shorja market, obliterating a building and setting shops on fire.
Eyewitnesses described debris and mannequins scattered in thick pools of blood on the floor of one building used as a clothes store.
Angry and distressed shopkeepers vented their frustration at the government's apparent inability to combat the wave deadly bombings.
"My store was completely burned, I lost $100,000 dollars. The government officials sit calmly in their offices, stuck on their chairs," said Mohammed Haider.
The Bab al-Sharqi blast half an hour earlier was caused by a bomb hidden in a bag planted near a popular take-away falafel restaurant.
The two markets are little over one kilometre (less than a mile) apart on east side of the River Tigris.
They have both been targets for bomb attacks in the past.