A spate of attacks against Shiite pilgrims and neighbourhoods in Iraq killed at least 61 people on Thursday as the country grapples with a weeks-long political row that has stoked sectarian tensions.

The violence, which wounded more than 100, was the worst since 67 people died on December 22, soon after the crisis erupted when Vice President Tareq al-Hashemi was charged with running a hit squad US troops pulled out.

Unlike the December attacks, which mostly hit a variety of neighbourhoods in Baghdad, Thursday's violence focused solely on Shiites.

It was quickly condemned by Iraq's parliament speaker Osama al-Nujaifi, a Sunni, as well as Iraq's Shiite-majority neighbour Iran.

"Political leaders fight each other for power, and we pay the price," said Ahmed Khalaf, a labourer who was near the site of attacks in the north Baghdad neighbourhood of Sadr City.

"How is it our fault if Hashemi is wanted, or someone else is wanted? Why should we pay instead of them?"

The worst incident saw at least 38 people killed by a suicide attack on the outskirts of the southern city of Nasiriyah as pilgrims were walking to the shrine city of Karbala for Arbaeen commemorations.

"Hospitals in Nasiriyah have received 38 killed and 68 wounded," said Hadi Badr al-Riyahi, head of the provincial health department in Dhi Qar, of which Nasiriyah is the capital.

Arbaeen marks 40 days after the Ashura anniversary commemorating the slaying of Imam Hussein, one of Shiite Islam's most revered figures, by the armies of the Caliph Yazid in 680 AD.

Five bomb attacks also struck two Shiite neighbourhoods in northern Baghdad, killed 23 people and wounded dozens more.

In Kadhimiyah, car bombs exploded at around 9:00 am (0600 GMT) at adjoining intersections, said officials from the interior and defence ministries.

The blasts killed 14 people and wounded 37 others, the defence official said, while the interior ministry source put the toll at 15 dead and 31 wounded.

Several nearby vehicles and shops, as well as the facade of a newly built hotel, were badly damaged.

"Where are the security forces?" shouted 60-year-old Ashur Abdullah at Al-Zahra intersection in Kadhimiyah.

"Where are the checkpoints? How did this happen here? The responsibility lies with the security forces."

In Sadr City, a booby-trapped motorcycle exploded at around 7:00 am near a group of day labourers waiting to pick up work, killing seven and wounding 20 others, the interior ministry official said.

A short time later, twin roadside bombs detonated near the district's main hospital as victims were being ferried in, killing two more people and wounding 15, the official said.

The defence ministry official confirmed the toll.

Security forces cordoned off the scenes of the blasts, and largely refused to allow journalists to enter, sparking the ire of residents.

"Why are you preventing the press and photographers from entering the scene?" shouted one man in Kadhimiyah who declined to be identified.

"Are you afraid that the world will see your failure?"

Prime Minister Nuri al-Maliki has backed off threats to fire ministers from the Sunni-backed Iraqiya bloc who have boycotted cabinet, the latest move in an apparent toning down of the crisis.

The standoff was sparked by a decision to issue an arrest warrant for Hashemi on terror charges.

Hashemi, who is holed up in the northern autonomous Kurdish region, denies the charges and his Iraqiya party has boycotted cabinet and stayed away when parliament re-opened on Tuesday.

Sunni Deputy Prime Minister Saleh al-Mutlak, also a member of Iraqiya, has decried Maliki as a dictator "worse than Saddam Hussein", and the premier has called for him to be sacked.

MPs were due to have considered that request on Tuesday, but the motion was never even discussed.

UN special envoy Martin Kobler, in a statement on Wednesday, "expressed concern about the current political stalemate in the country," and US Vice President Joe Biden has urged dialogue among top Iraqi leaders.

On December 18, US forces completed their withdrawal from Iraq, where there were once nearly 170,000 American troops on 505 bases.