A feud between Iraqi Sunnis and the Shiite authorities they accuse of marginalising their community is driving a deadly spike in violence, but will stop short of all-out conflict for now, experts say.

Attacks including bombings that ripped through worshippers in mosques and cut down shoppers in markets killed over 430 people in Iraq so far in May, 461 in April and 220 or more every other month this year, according to AFP figures.

Crispin Hawes, the Middle East and North Africa director for the Eurasia Group consultancy, said policies of Prime Minister Nuri al-Maliki that have politically isolated Iraqi Sunnis are the main factor behind the spike in violence.

The policies and resulting isolation have encouraged both "radicalisation" and passive tolerance of militants among Sunnis, he said.

"Pretty much since the last US soldier knocked the dust from his boots as he crossed the border (in late 2011), Maliki has gone after a succession of Sunni Arab politicians," Hawes said.

Maliki made an unsuccessful call on MPs to remove Deputy Prime Minister Saleh al-Mutlak, a Sunni who had said the premier was "worse than Saddam Hussein," the day that the last US soldiers left.

A day later an arrest warrant was issued for then-vice president Tareq al-Hashemi, another Sunni.

Hashemi fled Iraq and has since been sentenced to death multiple times in absentia for crimes including murder.

Maliki also sought to remove "Sunni Arab officers from the military (and) militarised, increasingly, population centres in western and northwestern Sunni Arab-dominated provinces in Iraq," Hawes said.

"It has been a consistent ratcheting up of pressure on that community that has progressively isolated and restricted their role in Iraqi politics," he said.

Discontent has been growing among Iraq's Sunni minority, which ruled the country from its establishment after World War I until US-led forces toppled dictator Saddam Hussein in 2003, bringing the Shiite majority to power.

Sunnis say Shiite authorities have marginalised their community and targeted them with unwarranted arrests and spurious terrorism charges.

Still-ongoing demonstrations erupted in Sunni-majority areas of Iraq in late December, and an April 23 security forces raid on a protest site that sparked clashes in which dozens died sent tensions soaring higher.

While the government has made some concessions aimed at placating protesters and Iraqi Sunnis in general, such as freeing prisoners and raising the salaries of Sunni anti-Al-Qaeda fighters, underlying issues have yet to be addressed.

John Drake, an Iraq specialist with risk consulting firm AKE Group, also pointed to Sunnis' feelings of disenfranchisement as the cause of the violence.

"There is an ongoing sense of marginalisation amongst the Sunni community, exacerbated by frustrations over a lack of jobs, development and improvements in standards of living," Drake said.

This provides increased motivation for Sunni militant groups to strike.

Militants "intent on widening their field of influence to include central Iraq and large parts of neighbouring Syria... appear to have increased the pace of their attacks," said Drake.

"If they target the government and security forces they may succeed in gaining sympathy from antagonised Sunni residents," he said.

Sunni militants, including those from Al-Qaeda's Iraqi front group, carry out frequent attacks.

Shiite militant groups such as Asaib Ahl al-Haq have meanwhile officially made their peace with the government, though some are thought to still be active, albeit more discretely.

It is unclear what direction the violence will take, but even the current heightened level of unrest is a far cry from the worst of Iraq's sectarian war from 2006 to 2008, when tens of thousands of people were killed.

Hawes said the rise in violence increases the likelihood of movement toward civil war or the disintegration of Iraq, but he believes an "intensified version of what we have now" to be the more probable outcome.

Maria Fantappie, an Iraq analyst with the International Crisis Group, said that "there will be a situation of continuous local clashes (between) protesters' armed factions and government-affiliated forces".

But this "violence will remain highly local, however, as the protesters' armed factions are many, and mostly disconnected from one province to another," she said.

"Conditions have worsened over recent weeks and the violence is strongly linked to core social divisions in the country," said Drake. "If the situation deteriorates further, it could certainly resemble a civil war."