Attacks, including 13 car bombs in mainly Shiite-populated areas of Iraq, killed at least 18 people Wednesday, highlighting the persistent danger from militants 11 years after American forces took Baghdad.

The latest violence is part of a protracted surge in nationwide bloodshed that has killed more than 2,400 people so far this year and sparked fears Iraq is slipping back into the all-out sectarian fighting of 2006-7.

The unrest has been driven principally by complaints among the Sunni Arab minority of mistreatment at the hands of the Shiite-led government and security forces, as well as spillover from the civil war in neighbouring Syria.

Eight car bombs struck seven separate areas of Baghdad around 10:00 am (0700 GMT), killing at least 11 people and wounding at least 49, security and medical officials said.

In the deadliest single attack in the capital, a car bomb exploded near a traffic police office in the Shiite shrine district of Kadhimiyah, killing at least three people and wounding at least eight.

Another car bomb exploded near a vegetable market, while main thoroughfares were also targeted.

Five more car bombs struck various areas of Wasit province, south of Baghdad, killing at least six people and wounding more than 40, a police officer and a health department official said.

And in the Saba al-Bur area north of Baghdad, two mortar rounds killed at least one person and wounded at least five.

The attacks highlight the persistent danger posed by militants in Iraq, 11 years after American troops took Baghdad.

The United States subsequently disbanded the Iraqi military and launched a "de-Baathification" programme targeting members of Saddam Hussein's party, both of which contributed to the rise of a bloody insurgency.

And while many Iraqis had high hopes after Saddam's 2003 overthrow, they have been dashed by years of deadly violence, widespread corruption and a persistent lack of basic services.

- Campaign in full swing -

The Wednesday bloodshed came a day after Iraq's security forces said they killed 25 militants near Baghdad.

Brigadier General Saad Maan said the fighters were part of the jihadist Islamic State of Iraq and the Levant (ISIL), and were planning to attack an army base they had attempted to hit last week.

Despite the tactical success, the killings illustrate the growing ambition of ISIL militants seeking to fight their way into Baghdad, as an April 30 general election looms.

It is the first election to the Iraqi parliament since US forces left at the end of 2011, although both provincial elections and an election to the Kurdish regional parliament were held last year.

Campaigning is in full swing, with colourful political posters crowding roadsides across the Iraqi capital.

One sign hangs from a destroyed building in central Baghdad, while others surround the plinth at Firdos Square from which a statue of Saddam was toppled on April 9, 2003, in one of the most famous images of the dictator's fall.

The United Nations has warned that the election campaign will be "highly divisive", as party leaders appeal to their sectarian political bases.