Nuri al-Maliki is bidding for a third term as Iraqi premier on Wednesday without any obvious challenger, in marked contrast to the 2010 election when he faced an ex-premier in a tight race.

Supporters of the prime minister, in power since 2006, have cultivated an image of a strong leader fighting off violent extremists and outside powers.

But his critics have lambasted the 63-year-old Shiite Arab for what they say are insufficient improvements in basic services and pervasive corruption.

"For Maliki, it is a matter of life or death," said Aziz Jabr, a political science professor at Baghdad's Mustansiriyah University.

"A third term will mean preserving all the benefits of being in power, but losing means giving up all of that."

But Jabr added "the fissures that have emerged in the Shiite community in the past four years have not helped highlight another Shiite leader against Maliki."

Though not codified, Iraq's leaders have established a de facto agreement whereby the prime minister is a Shiite, the president a Kurd, and the speaker of parliament a Sunni Arab.

Wednesday's parliamentary election, the first since US troops pulled out in late 2011, comes with violence at its worst since Iraq's brutal sectarian war between Sunnis and Shiites in 2006-2008, and with anti-government fighters in control of the town of Fallujah a short drive from Baghdad.

In addition to the near-daily bloodshed, voters have a long list of grievances, ranging from power rationing and poor sewerage to high unemployment and rampant graft.

- No obvious challenger -

Despite these issues, the month-long election campaign has centred around Maliki's bid for a third term, something he said in February 2011 he did not want to pursue.

Though his critics have railed against him, a fractious and divided opposition has meant that he remains the frontrunner to retain the premiership.

A potential replacement for Maliki "is the key question" in these elections, said a Western diplomat who spoke on condition of anonymity.

"It's different from 2010... People haven't formed alliances that offer a clear cut choice ahead of the elections, because everybody is waiting to see how they will do during the elections.

"Once the votes are in, we may see people emerge."

The landscape for the April 30 election differs markedly from 2010, when Maliki faced off with Shiite ex-premier Iyad Allawi, who at the time headed a secular Sunni-backed coalition.

Allawi's Iraqiya bloc narrowly edged out Maliki, but the incumbent still managed to manoeuvre to secure the premiership by winning the backing of powerful neighbour Iran and allying with other Shiite parties after the election.

Iraqiya has since fractured into multiple factions, and Maliki's principal Shiite rival in the 2010 polls has also broken down into several blocs.

At the time, the premier touted gains made in security, when violence was close to multi-year lows.

- 'Tackling extremists' -

Security is again at the centre of the debate, but with Maliki now arguing that he is leading a fight against Sunni extremists.

"Maliki is using the security crisis to shift the debate from public dissatisfaction with governance," said Michael Knights, a fellow at the Washington Institute for Near East Policy.

"If he succeeds, the security crisis could greatly benefit him."

Anti-government fighters currently control all of Fallujah and are battling Iraqi security forces in other parts of the western desert province of Anbar.

Maliki has pointed the finger at Saudi Arabia and Qatar for supporting militancy in Iraq and blamed fallout from the civil war in Syria for the surge in bloodshed.

Analysts and diplomats have urged the premier to reach out to Iraq's Sunni Arab minority and address its complaints to undercut support for militants.

Ahead of the election, though, Maliki and other Shiite leaders have been loath to be seen to compromise.

With at least some Sunni backing crucial to any realistic bid for a third term, that may hamper him.

"The image of the strongman that Maliki is trying to cultivate will not benefit him among Sunnis," said Jabr.

"The Sunnis will not accept a third term for Maliki, after four years of campaigning against him."