Iraq car bombs kill 15

Iraqi armed tribesmen pose for a picture on the back of a truck in a road north of Ramadi, on May 18, 2013. Two car bombs went off in the area in a spike of violence

Three car bombs, including two blasts by suicide attackers, killed 15 people in Iraq on Friday, the latest in a spike in violence that has sparked fears of all-out sectarian war.

Two suicide car bombs struck a police checkpoint near Ramadi, the capital of mostly Sunni Anbar province, killing at least five policemen and wounding eight others, officials said.

And north of Baghdad, a parked vehicle rigged with explosives detonated in the restive town of Muqdadiyah, killing 10 Iranian pilgrims and wounded 30 others.

The blast occurred as the pilgrims' bus passed through the town en route from the Iranian border to the Shiite holy city of Najaf.

Najaf, which lies south of Baghdad, is home to a shrine to a revered figure in Shiite Islam.

Shiite Muslims visiting shrines and religious sites form the backbone of Iraq's tourism industry, with the vast majority of pilgrims coming from Iran.

When completing a tour of Iraq's key Shiite religious sites, pilgrims typically visit Najaf, nearby Karbala, Baghdad, and Samarra, the latter of which lies north of the capital.

Sunni militants, including those linked to Al-Qaeda, view Shiites as apostates and often target them. However, no group immediately claimed responsibility for Friday's bombing.

Attacks in Iraq have risen sharply, with May the deadliest month since 2008, as persistent political disputes have given fuel and room for militants to increase their activities.

There has been a heightened level of violence since the beginning of the year, coinciding with rising discontent among the Sunni Arab minority that erupted into protests in late December.

The UN envoy to Iraq has warned that the violence is "ready to explode".