The bombings in Baghdad and north and west Iraq raise serious concerns about the ability of the country's security forces to protect voters during Wednesday's general election, when more than 20 million Iraqis are eligible to vote.
They come amid a protracted surge in violence and fears the country is edging towards all-out conflict.
Attackers wearing suicide belts hit polling centres in Baghdad and cities north of the capital, while roadside bombs struck military convoys and targeted journalists covering the polling.
At a voting centre in western Baghdad where six security members were killed, ambulances rushed to and fro, collecting the wounded, as soldiers cordoned off the street and ushered passersby away, an AFP journalist said.
Attacks elsewhere left 14 dead overall - all members of the security forces - officials said.
In the main northern city of Mosul, meanwhile, six journalists were wounded as a bomb went off while they were travelling in a military vehicle to cover police and troops voting.
The blasts shattered an early morning calm, when soldiers and policemen had queued outside voting centres amid tight security across Baghdad and around the country as polls opened, leaving with the traditional purple ink-stained finger indicating they had voted.
Prime Minister Nuri al-Maliki, lambasted by critics for allegedly consolidating power and targeting minority groups amid a deterioration of security, is bidding for a third term in the polls with Iraqis frustrated over poor basic services, rampant corruption and high unemployment.
The month-long campaign has seen Baghdad and other cities plastered with posters and decked out in bunting, as candidates have taken to the streets, staged loud rallies and challenged each other in angry debates.
'For sake of Iraq'
I have come to vote "for the sake of Iraq, and to change the faces who have not served Iraq," said Ahmed, a policeman wearing civilian clothes who was queuing at a polling station in central Baghdad and declined to give his full name.
Along with more than 800 000 members of the security forces who are eligible to vote at upwards of 500 polling centres nationwide, hospital and prison staff, patients and inmates were also voting on Monday.
The election commission meanwhile said that more than 60 000 ballots had so far been cast in out-of-country voting which continues through Monday.
Attacks on candidates, election workers and political rallies have cast a shadow over the vote, however, and parts of the country that have been out of government control for months will not see any ballots cast.
Authorities have announced a week of public holidays to try to bolster security for the election.
The unrest is the latest in a months-long surge in violence that has claimed nearly 3 000 lives already this year, while anti-government fighters have held control of an entire town a short drive from Baghdad since the beginning of the year.
Although voters have a long list of grievances, from poor electricity and sewerage services to pervasive graft and difficulties securing jobs, along with the near-daily violence, the election has centred around Maliki and his efforts to retain power.
His opponents, who span the communal spectrum, accuse him of shoring up his power base, while minority Sunnis in particular say the 63-year-old Shiite Arab discriminates against them.
Maliki contends that foreign interference is behind deteriorating security and complains that he has been saddled with a unity government of groups that snipe at him in public and block his legislative efforts.
But according to analysts and diplomats, with a fractious and divided opposition and no clear replacement, he remains the frontrunner in the first national election since 2010, and the first since US troops withdrew in December 2011.
No single party is likely to win an absolute majority, however, and as in previous elections, coalition talks are expected to take months as the main positions of power are typically negotiated in one encompassing package.