Iraq has held a democratic vote to choose a leader with no foreign troops present for the first time ever.

Shia Prime Minister Nuri al-Maliki seeks to hold power for a third term in a country again consumed by sectarian bloodshed.

Since the last US soldiers pulled out in 2011 eight years after toppling dictator Saddam Hussein, Iraq has descended back into extreme violence.

Hundreds of civilians are killed each month by al Qaeda-inspired Sunni insurgents, and Shia militia once more taking revenge.

Voters are choosing from nearly 10,000 candidates for 328 seats in parliament, from political parties that range from Islamists to liberals and communists.

But even more than in the last election four years ago, parties with sectarian and ethnic agendas are expected to lead the field, potentially exacerbating the divisions that underlie the worsening carnage.

But despite the myriad parties, the election is widely seen as a referendum on Mr Maliki who has governed for eight years.

He says he is the only politician with enough strength to battle insurgents; his opponents say his bullying of his political enemies has brought Iraq to the verge of collapse.

Two different elections unfolded across Iraq today: one in predominantly Shia areas of the country, where people were voting for the figure they thought best suited to defeat the al-Qaeda offshoot the Islamic State of Iraq and the Levant (ISIL); the other in Sunni regions and neighbourhoods in Baghdad, where people fear both the Shia-led security forces and ISIL.

In Baghdad, roads were dotted with military checkpoints and people walked on foot to the polling stations.

Humvees flanked the voting centres. Razor wire sealed off the areas as people passed multiple checkpoints to vote.S oldiers and police swarmed the street.

ISIL, which is leading Sunni insurgencies in both Iraq and Syria, had threatened to kill anyone who votes.

At least 12 people were reported killed, including eight blown up by suicide bombers at polling stations in Diyala and Salahuddin, provinces north of Baghdad with large Sunni populations.

Four soldiers were killed by a bomb while racing to a polling station surrounded by gunmen.

In the northern city of Mosul, where ISIL has widespread influence, many people were afraid to vote and some polling stations did not open, said Marwan al-Ani, a professor at Mosul University.

Baghdad itself was quieter than four years ago.

Mr Maliki was among the first to vote, at a hotel next to the fortified Green Zone where the government is based. He urged people to follow suit despite security threats.

"I call upon the Iraqi people to head in large numbers to the ballot boxes to send a message of deterrence and a slap to the face of terrorism," Mr Maliki told reporters.