Violence across Iraq, including shelling and clashes in a rebel-held city on Baghdad's doorstep, have killed 37 people amid a protracted surge in bloodletting with polls looming next month.

In the city of Fallujah, 60km west of the capital, government-led shelling and fighting between soldiers and gunmen killed 15 people and wounded 40, according to Ahmed Shami, the chief medic at the city's main hospital.

The violence erupted just after midnight on Wednesday as sporadic shelling targeted northern, eastern and southern neighbourhoods of the city.

Speaking to the AFP news agency tribal leaders in the city confirmed the doctor's account.

"Shelling first targeted several areas...and clashes also happened," Mohammed Saleh, a leader of the Bijari tribe, said.

Mahmud al-Zobaie, a leader of the Zoba tribe, said many people were "killed and wounded" and homes were "damaged because of the shelling."

Security forces have periodically shelled neighbourhoods of Fallujah in recent months, arguing that they are targeting anti-government fighters holding the city.

Fallujah has been outside of government control with the Iraqi army prevented from entering by local Sunni tribesmen who are opposed to the Shia-dominated government of Prime Minister Nouri al-Maliki.

In January, anti-government fighters took control of the city and overran parts of nearby Ramadi, the capital of the predominantly Sunni province of Anbar before security forces managed to wrest back control.

Maliki previously vowed to eliminate "all terrorist groups" from Anbar and said his government would end disunity, in the province.

Upcoming elections

Elsewhere in Iraq, attacks killed 22 people on Wednesday, security and medical officials said.

North of the capital Baghdad, four policemen were killed and four wounded when they tried to investigate a parked car in Ishaqi that had a booby-trapped corpse inside.

Violence in and around Baghdad, meanwhile, killed a dozen people, and attacks in the restive provinces of Diyala, Nineveh and Kirkuk - all north of the capital - killed six.

Iraq has seen an increase in violence as authorities struggle with the country's worst unrest since 2008, as the country emerged from Sunni-Shia sectarian violence that killed tens of thousands and displaced countless others.

With elections due to be held on April 30, analysts and diplomats have urged the Shia-led authorities to do more to reach out to the disaffected Sunni community.

The violence, in which more than 2,000 people have died already this year, has been primarily driven by discontent in the minority Sunni Arab community, that alleges mistreatment at the hands of the Shia-led government and security forces, and by the civil war raging in neighbouring Syria.