A series of car bombs near Shiite mosques targeting worshippers attending weekly prayers killed at least 18 people on Friday, the latest in a spike in unrest ahead of Iraq's first polls since 2010.

The blasts, which also wounded more than 100 people, struck within an hour of each other in the Baghdad neighbourhoods of Binook, Qahira, Zafraniyah and Jihad, as well as in an area of southern Kirkuk city.

No group immediately claimed the attacks, but Sunni militants linked to Al-Qaeda frequently target Shiite Muslims whom they regard as apostates and supporters of the Shiite-led government.

In Baghdad, four car bombs were detonated near Shiite mosques across the capital, leaving at least 14 people dead and 35 wounded, security and medical officials said, speaking on condition of anonymity.

And in Kirkuk, which lies 240 kilometres (150 miles) north of the capital, four people died and 71 were hurt by another car bomb targeting a Shiite mosque, provincial health chief Sadiq Omar Rasul said.

"I was praying inside the Husseiniyah (Shiite mosque) during Friday prayers," said Salim Aziz al-Bayati, one of the worshippers who was wounded by the attack at the mosque.

"Then, all of a sudden, a great, horrible explosion happened, and the roof fell on our heads."

Also among the wounded was Mohsen al-Battat, a representative of Iraq's most revered Shiite cleric Grand Ayatollah Ali Husseini al-Sistani, who had been leading the prayers.

Bayati continued: "I saw the imam (Battat) was lying on the floor, and blood was on everyone's bodies. When they (paramedics) were taking me away, I saw a fire covering the Husseiniyah, and nearby houses and cars."

In Baghdad's Qahira neighbourhood, an AFP reporter described seeing pools of blood on the ground with massive damage to nearby cars, houses and shops. Several residents were crying as soldiers imposed a heavy security presence in the area.

Security forces elsewhere in the capital threatened to detain AFP journalists for attempting to film and take photographs of the aftermath of the bombings.

The attacks come amid a spike in violence nationwide as the country prepares for its first elections in three years -- provincial polls that will be held in 12 of Iraq's 18 provinces on April 20.

Questions have been raised over the credibility of those polls as elections have been postponed in two provinces roiled by months of protests, and at least 11 candidates have been killed.

The polls are seen as a key barometer of support for Prime Minister Nuri al-Maliki as he grapples with criticism from within his unity cabinet and protests in the minority Sunni Arab community.

The attack in Kirkuk is also likely to raise tensions in a city at the heart of a long-running dispute over territory between the central government in Baghdad and the country's autonomous Kurdistan region.

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

Violence is down from its peak in 2006 and 2007 but attacks remain common, and this month's death toll of 259 is already the highest since August, according to figures compiled by AFP.

The latest violence comes days after the 10th anniversary of the US-led invasion of Iraq, which ousted dictator Saddam Hussein and had sought to establish a stable, democratic ally in his place but instead unleashed brutal violence and endless political disputes.