Story Highlights• NEW: At least 15 people die in Wednesday attacks on Shiite pilgrims in Baghdad
• Bombings follow two days of attacks that left scores dead or wounded
• Deadliest attack occurred in double suicide bombings in Hilla; at least 114 killed
• Gunmen attack prison near Mosul, freeing detainees
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HILLA, Iraq (CNN) -- Attacks on Shiite pilgrims en route to the Iraqi holy city of Karbala continued into a third day as bombings killed 15 people Wednesday in Baghdad, police said.
A suicide car bomber struck an Iraqi police checkpoint as pilgrims walked in southwestern Baghdad's Saydiya neighborhood, killing eight -- seven police and a pilgrim -- and wounding 25 -- 15 police and 10 pilgrims, a Baghdad police official said.
Earlier Wednesday, attackers detonated a roadside bomb before opening fire on pilgrims, killing at least seven and wounding 14 others in the capital's predominately Sunni Dora district, the official said.
Iraqi security forces have been deployed into Sunni neighborhoods in Baghdad to secure the roads for the Shiite pilgrims.
The blasts followed two days of bombings and small-arms attacks that left scores dead or wounded.
In the deadliest attack, suicide bombers targeted Shiite pilgrims Tuesday in the central city of Hilla, killing 114 people and wounding 147 others, police said. Forty of the injured are in critical condition, a Hilla police official said.
Two bombers struck the crowd of pilgrims on foot in the mostly Shiite city, about 80 miles (128 kilometers) south of Baghdad, the official said. (Watch how pilgrims have become a popular target )
Many of the pilgrims were from Iraq's southern provinces, and were walking on a main road through the city's downtown.
Pilgrims are traveling through Hilla en route to Karbala for Arbayeen, a religious gathering for Shiites that falls on Saturday.
Arbayeen marks the end of a 40-day mourning period that begins on Ashura, the anniversary of Imam Hussein's death. Imam Hussein is the grandson of the Prophet Mohammed and is considered by Shiites to be the prophet's successor.
Karbala is about 25 miles (40 kilometers) east of Hilla.
The United States vowed to stop "atrocities against the Iraqi people," according to a joint statement from Zalmay Khalilzad, the U.S. ambassador to Iraq, and Gen. David Petraeus, commander of the U.S.-led multinational forces.
"Attacking innocent pilgrims who are participating in a religious observance is unconscionable," the statement said.
Scattered attacks on journey to Karbala
In addition to Tuesday's double suicide bombing in Hilla, authorities said other scattered attacks in the nation left dozens of Shiites dead as they made their way to Karbala.
Gunmen attacked a pair of minibuses, killing two Shiite pilgrims en route to the commemoration and wounding six others in Latifiya, about 25 miles (40 kilometers) south of Baghdad.
Shortly after the first attack, gunmen opened fire on a group of pilgrims walking in Latifiya, killing one and wounding seven others.
A roadside bomb blast later killed five Iraqi police officers on patrol in eastern Baghdad's Aubaydi district.
Also, a roadside bomb exploded near a fuel tanker, killing two people and wounding four others on the Sarrafiya Bridge in northern Baghdad.
In addition, a car bomb killed four Shiite pilgrims and injured 14 others in Baghdad's Yarmouk district.
In Baghdad's southern Dora district, a car bomb killed 12 pilgrims and wounded 38 others.
A car bomb in western Baghdad's Qadssiya neighborhood killed one pilgrim and injured three others.
Gunmen attacked a minibus in the Mahdiya neighborhood of southern Baghdad, killing eight pilgrims.
On Monday, at least nine pilgrims were killed and 24 wounded in a series of similar attacks.
Prison raid in Mosul
Gunmen launched an attack Tuesday on a prison outside the northern Iraqi city of Mosul, freeing a number of detainees, an Iraqi Interior Ministry official and a Mosul police official said.
Iraqiya state TV said that 140 detainees managed to escape after the attack, but Gen. Mohammed al-Wagaah of the Mosul police said the gunmen freed at least 47 detainees and prisoners.
The gunmen clashed with prison guards at Badosh prison, about 20 miles (30 kilometers) west of Mosul, the officials said.
The Iraqi army and police are conducting a search to recapture the escapees, and the prison has been returned to government control.
Separately, police and hospital officials said that a car bomb struck an Iraqi army patrol Tuesday in southern Mosul. At least five people were killed, including one Iraqi soldier, and 18 people were wounded, including two Iraqi soldiers.
CNN's Jennifer Deaton, Basim Mahdi and Mohammed Tawfeeq contributed to this report.