In Madaen, southeast of Baghdad, attackers blasted a police station with grenade and mortar fire before dawn on Wednesday, killing four policemen in the second such attack in two days.
Police said they detained about 70 people in raids afterwards.
Police also reported the discovery of six more bodies on the streets of the capital on Wednesday, all apparent victims of the bloodshed between majority Shia and once-dominant Sunnis which some Iraqi officials fear could expand into open warfare.
The pilgrims were driving home a day after celebrating a major Shia festival in Kerbala, south of the capital.
"We were on the highway when suddenly four cars stopped near us and began shooting," a man who gave his name as Allawi said from his hospital bed.
|Four policemen were killed when |
the Madaen station was attacked
Police said 22 pilgrims were wounded and one was killed in an attack on their open-back truck in western Baghdad.
In a second incident in the same area, one Shia was killed and 18 were wounded when their bus was hit by machine-gun fire.
A police patrol rushing to the scene of one attack was ambushed by attackers who fired a rocket-propelled grenade, killing two policemen and wounding four, police said.
Police station attacked
Police said the commander of a special police unit, Colonel Ahmed Jabar, was among four policemen killed in Wednesday's attack on the Madaen police station.
They said most of the 70 people detained in the crackdown by interior ministry forces after the blast lived locally. There was no word on any casualties among the attackers.
On Tuesday, dozens of attackers hit a police post and jail at Miqdadiya, northeast of Baghdad, killing at least 22 people and freeing 30 prisoners.