More than 60 people were killed in a series of car bomb explosions targeting Shi'ite Muslims across Iraq on Monday, police and medics said, part of the worst sectarian violence since US troops pulled out in December 2011.

The attacks brought the number killed in sectarian clashes in the past week to over 200, and tensions between Shi'ites, who now lead Iraq, and minority Sunni Muslims have reached a point where some fear a return to all-out civil conflict.

No group claimed responsibility for the bombings. Iraq is home to a number of Sunni Islamist insurgent groups, including the al Qaeda-affiliated Islamic State of Iraq, which has previously targeted Shi'ites in a bid to provoke a wider sectarian confrontation.

Nine people were killed in one of two car bomb explosions in Basra, a predominantly Shi'ite city 420 km southeast of Baghdad, police and medics said.

"I was on duty when a powerful blast shook the ground," said a police officer near the site of that attack in the Hayaniya neighbourhood.

"The blast hit a group of day labourers gathering near a sandwich kiosk," he added, describing corpses littering the ground. "One of the dead bodies was still grabbing a blood-soaked sandwich in his hand."

Five other people were killed in a second blast inside a bus terminal in Saad Square, also in Basra, police and medics said.

In Baghdad, at least 30 people were killed in car bomb explosions in Kamaliya, Ilaam, Diyala Bridge, al-Shurta, Shula, Zaafaraniya and Sadr City - all areas with a high concentration of Shi'ites.

A parked car bomb also exploded in the mainly Shi'ite district of Shaab in northern Baghdad, killing 12 people and wounding 26 others, police and hospital sources said.

In a separate incident, police said a parked car blew up near a bus carrying Shi'ite pilgrims from Iran near Balad, 80 km north of Baghdad, killing five Iranian pilgrims and two Iraqis who were traveling to the Shi'ite holy city of Samarra.

In the western province of Anbar, the bodies of 14 people kidnapped on Saturday, including six policemen, were found dumped in the desert with bullet wounds to the head and chest, police and security sources said.

When Sunni-Shi'ite bloodshed was at its height in 2006-07, Anbar was in the grip of al Qaeda's Iraqi wing, which has regained strength in recent months.

In 2007, Anbar's Sunni tribes banded together with US troops and helped subdue al Qaeda. Known as the "Sahwa" or Awakening militia, they are now on the government payroll and are often targeted by Sunni militants as punishment for co-operating with the Shi'ite-led government.

Three Sahwa members were killed in a car bomb explosion as they collected their salaries in the city of Samarra, north of Baghdad, police said.

Iraq's delicate intercommunal fabric is under increasing strain from the conflict in neighbouring Syria, which has drawn Sunni and Shi'ite Muslims from across the region into a proxy war.-Reuters