A car bomb that exploded in a Baghdad district lined with book shops has killed at least 26 people and wounded scores more.
A police source said 54 more were injured following the attack in Mutanabi Street.
He added that a second bomb exploded in another street nearby around the same time, although it was not clear how many casualties there were from that explosion.
Smoke rises over Baghdad after this morning's car bomb attacks in the Mutanabi area
Iraqi and US forces are in the third week of a major security crackdown in Baghdad aimed at stemming sectarian violence.
A big increase in the number of troops on the streets and checkpoints appears to have reduced killings, but US commanders say car bombs remain a major problem.
More than 1,000 US and Iraqi troops yesterday carried out searches in the Shia militia bastion of Baghdad's Sadr City, stronghold of the Mehdi army of anti-American cleric Moqtada al-Sadr.
Sadr, a key supporter of Shia Prime Minister Nuri al-Maliki, has criticised the crackdown and said it will fail as long as US forces are involved.
Many members of the Mehdi army are either lying low or have left Baghdad, unlike in 2004 when the militia twice rose up against US forces. Washington calls the Mehdi army the greatest threat to Iraq's security.
Residents in Sadr City said checkpoints that used to be manned by Mehdi army fighters had melted away, replaced by Iraqi army and police.