Baghdad , Iraq ( CNN ) -- A series of bomb attacks disrupted voting as the polls opened in Iraq 's national elections Thursday , leaving a total of 12 people dead and another 47 wounded . There had been warnings of insurgent attacks around the vote , which is intended to install a 325-member parliament and select Iraq 's next government . Early voting began Thursday for those who will be unable to cast their ballots in Sunday 's election , including thousands of army and security personnel . In the first of three attacks , five civilians were killed and 22 injured when a bomb went off in the Hurriya neighborhood of northern Baghdad , an interior ministry official said . The bomb had been placed about 500 meters ( 546 yards ) away from a polling center that was going to be used Sunday , but was not open for Thursday 's early voting , the official said . It was not clear whether the polling center was the target , as hundreds of them will be open Sunday , most within 500 meters of each other . Are you voting in Iraq ? Send us your story , images . In the al-Mansour district of western Baghdad , at least three people were killed and 25 wounded in a suicide bombing outside a polling center , an interior ministry official said . Most of the casualties were Iraqi army soldiers , the official said . The suicide bomber struck the forces as they were assembling outside the polling center to vote , the official said . The bomber was disguised as an Iraqi police officer and stopped before reaching the polling center , according to a U.S. military statement . A second suicide attacker struck another Iraqi army gathering on its way to vote in the Bab Al-Muadham area of central Baghdad , the ministry said . Four soldiers were killed and 10 others wounded in the attack . Thousands of army and security personnel are among those taking part in Thursday 's voting , which is for those who will unable to cast their ballots Sunday . Others voting Thursday include detainees , hospital staff and patients . As many as 700,000 security forces are expected to vote , according to the U.N. Assistance Mission to Iraq . There was heavy security around polling centers Thursday , with Iraqi forces blocking streets around them and not allowing any vehicles in . At one polling center , voters and personnel entering on foot had to go through a number of body searches . Iraqi Air Force helicopters have been active in the skies all day and snipers can be seen on rooftops near polling centers . A public holiday began Thursday and will run until Monday because of the elections . U.S. and Iraqi officials had warned of expected violence ahead of the vote . On Wednesday , three suicide attacks in Baquba , northeast of the capital , killed at least 33 people and wounded dozens more . It is Iraq 's fifth nationwide vote since 2003 , but only the second for a full four-year-term parliament with its 325 seats . `` The conduct and outcome of the election will be the most decisive moment for Iraqis ' future since 2003 , '' Ad Melkert , the head of the U.N. mission in Iraq , said Monday . Authorities on Iraqi state television announced special measures for the days surrounding the vote . Since Monday , there has been a ban on motorcycles and bicycles in Baghdad until further notice , and a two-day ban on any vehicles in cities begins Sunday , they said . Provincial borders will be sealed , preventing movements between provinces , from Saturday to Monday . And international borders and all airports will be shut from midnight Saturday . A curfew will be in place in cities from midnight to 5 a.m. on Saturday , Sunday and Monday , officials said . Civilians may not carry weapons on those days , they said . CNN 's Jomana Karadsheh and Yousif Bassil contributed to this report .
NEW : 12 people dead and dozens wounded in series of bomb attacks . Attacks coincide with early voting in Iraq 's national election . Security is tight after insurgent groups vowed to boycott the election . Vote will install a 325-member parliament and form Iraq 's next government .