Two suicide car bombs have hit central Baghdad within hours of each other, killing at least five people.
Most of the dead and injured are said to have been in the convoy
The dead are reported to be from a police convoy targeted in the Rashid Street shopping district, after an earlier blast near a checkpoint.
The BBC's Mike Donkin in Baghdad says the blasts came amid a massive security crackdown across the capital city.
Earlier, dozens of people were killed in US air strikes on the restive city of Falluja, west of Baghdad.
Witnesses near Rashid Street said an attacker drove up to a convoy of six police vehicles before blowing up his car at about 1230 local time (0830 GMT).
A large crater was gouged in the road and US troops and Iraqi police tried to clear the area, as ambulances rushed to treat the wounded.
Reuters news agency quoted a government official as saying up to 13 people had been killed.
About 20 people were injured in the blast.
"The suicide bomber was driving a Chevrolet Malibu. He smashed his car against the police vehicle," interior ministry spokesman Adnan Abdul Rahman was quoted as saying by the AFP news agency.
"Five of my police colleagues were killed and all eight of our patrol cars were damaged," First Lieutenant Jafaar Hussein, his shirt drenched in blood, told AFP.
Correspondents say the Rashid Street area of Baghdad is usually teeming with shoppers, but is traditionally less crowded on a Friday, the first day of the weekend in Iraq.
The attack on the convoy was near Haifa Street, where nearly 50 people died in a bombing on Tuesday.
It came soon after US and Iraqi forces mounted a major security operation against fighters in Haifa Street, using tanks to block off the area amid continuing gun battles.
Iraqi officials said 63 suspected militants, including Syrian, Egyptian and Sudanese nationals, were arrested during an early morning sweep of the area.
Our correspondent says fighters have been using Haifa Street to mount rocket and mortar attacks on the nearby international zone.
He adds that another aim of the operation is to stop insurgents from other parts of Iraq moving in to consolidate resistance in the capital itself.
The earlier car-bomb blast came as suspected suicide attackers drove towards a security checkpoint near the Tigris river that flows through the heart of Baghdad.
Reports say the car blew up when it was fired on.
The Baghdad attacks came hours after the US said it killed up to 60 militants in air strikes aimed at suspected terror mastermind Abu Musab al-Zarqawi in and around Falluja.
The health ministry said 44 people had been killed.
Hospital medics quoted by news agencies said many were civilians, including women and children.
Falluja and surrounding areas have been a hotbed of resistance to US forces and the interim Iraqi government.