At least 72 people have been killed in a coordinated wave of attacks across Iraq targeting Shi'ite Muslim pilgrims gathered for an annual religious commemoration. Nearly 260 other people were wounded in one of the bloodiest days since U.S. troops withdrew from the country.

Most of the bombs exploded in Baghdad and the southern Iraqi cities of Hilla, Karbala and Haswa – predominantly Shi'ite areas that have been targeted before by Sunni Islamist insurgents.

Nearly 30 people were killed when four blasts hit pilgrims marching in Baghdad to mark the death anniversary of revered Shi'ite religious figure Imam Moussa al-Kadhim, a great-grandson of the Prophet Muhammad.

In Hilla, two car bombs left at least 20 people dead and nearly 40 injured. A parked car bomb also exploded near pilgrims in the Shi'ite holy city of Karbala, killing two and wounding 22 others. Other explosions targeted Iraqi Kurds in the north.

The pilgrimage culminates on Saturday, raising the prospect of further violence in the coming days.

The latest bombings and shootings coincide with an Iraqi political crisis in which minority Sunni and Kurdish lawmakers have been trying to unseat Shi'ite Prime Minister Nouri al-Maliki, accusing him of monopolizing power in Shi'ite hands.

Baghdad's central government is also caught in a long-running fight with the autonomous Kurdistan region over disputed land and oil claims.

No group has claimed responsibility for Wednesday's attacks. But a Baghdad-based reporter for VOA's Kurdish Service said it is likely the Islamic State of Iraq, an umbrella organization that includes al-Qaida's local affiliate, is trying to exploit the country's political turmoil.

He said the bloodshed is not likely to stop pilgrims from making their journeys to Shi'ite holy sites, and that Iraqi security forces are on high alert with curfews declared in some cities.

Iraqi parliament speaker Osama al-Nujaifi condemned the attacks as an attempt “to provoke sectarian strife.”

The targeting of Shi'ite pilgrims was a common tactic during the vicious civil war that tore Iraq apart in 2006 and 2007.

Violence in Iraq has declined since then, but attacks remain common, especially in Baghdad.