More than a dozen bombings across Iraq on Monday killed at least 19 people in the latest in a spike in violence just days before the country's first elections since US troops withdrew.

The violence, which struck during morning rush hour amid tightened security ahead of the polls, also wounded almost 200 people and raises further questions about the credibility of the April 20 vote, seen as a key test of Iraq's stability and its security forces' capabilities.

A total of 14 election hopefuls have already been murdered and just 12 of the country's 18 provinces will be taking part.

Officials said 18 car bombs exploded Monday in Baghdad, the northern cities of Kirkuk, Tuz Khurmatu and Tikrit, the central city of Samarra, and Hilla and Nasiriyah south of Baghdad. Three roadside bombs also hit Baquba, north of the capital.

No group immediately claimed responsibility for the attacks, but Sunni militants linked to Al-Qaeda frequently attack both government targets and civilians in a bid to destabilise the country, and have reportedly sought to intimidate candidates and election officials ahead of polls.

The deadliest attacks were in Baghdad, where six car bombs struck in five neighbourhoods across the capital despite tougher checkpoint searches and heightened security.

Eight people were killed and 48 wounded in the capital, security and medical officials said, and an AFP journalist reported that officials in a tow truck were checking for suspicious vehicles in central Baghdad in the wake of the violence.

In Tuz Khurmatu, which lies 175 kilometres (110 miles) north of Baghdad, six people were killed and 60 wounded by three near-simultaneous car bombs, according to a provincial council member and a doctor.

And in Kirkuk, four people were killed and 19 wounded by another trio of car bombs, provincial health chief Sadiq Omar Rasul said.

Explosions elsewhere in Iraq killed one person and wounded 64 people.

Kirkuk and Tuz Khurmatu lie at the centre of a tract of disputed territory that stretches from Iraq's eastern border with Iran to its western frontier with Syria.

The swathe of land is claimed by both the mostly-Arab government in Baghdad and the three-province autonomous Kurdistan region of north Iraq.

The dispute is often cited by officials and diplomats as the biggest long-term threat to Iraq's stability.

Soldiers and policemen cast their ballots for the provincial elections on Saturday, a week ahead of the main vote, the country's first since March 2010 parliamentary polls. It is also the first election since US troops withdrew from Iraq in December 2011.

The election also comes amid a long-running crisis between Prime Minister Nuri al-Maliki and several of his erstwhile government partners, which officials and diplomats say give insurgent groups exploit by using the political differences to enhance their room for manoeuvre on the ground.

More than 8,000 candidates are standing in the elections, with 378 seats on provincial councils up for grabs. An estimated 16.2 million Iraqis are eligible to vote, among them about 650,000 members of the security forces.

Although security has markedly improved since the height of Iraq's confessional conflict in 2006-2007, 271 people were killed in March, making it the deadliest month since August, according to AFP figures.