Twelve people were killed in Baghdad Thursday, including seven soldiers and police blown up by suicide bombers, days before a poll that will test Iraq's prospects for stability as US troops prepare to leave. Thirty-five soldiers and police were also wounded when two attackers with explosive belts struck at centers where security forces were voting early, an Interior Ministry source said. A powerful explosion earlier killed five civilians and wounded 22 in Baghdad's northwestern district of Hurriya. The assailants seemed bent on disrupting the special voting by troops, police, detainees and the sick, hoping to undermine the government and deter voters from turning out on Sunday. The election is Iraq's second for a full four-year parliament since the 2003 US-led invasion. Thursday's attacks occurred despite tight security measures imposed to guard the 950,000 people eligible to vote early, most of them from Iraq's 670,000-strong security forces. Foreign oil firms starting to invest in Iraq's vast energy resources are watching to see if security gains can be sustained against Shiite militias, which the US military says are backed by Iran, and Sunni militants like Al-Qaeda. The Al-Qaeda-affiliated Islamic State of Iraq group threatened last month to prevent Sunday's election at any cost, using primarily “military” means to stop what it called a farce aimed at cementing Shiite domination over Sunnis. Security - and broken pledges - were high among issues listed by policemen voting in the Shiite city of Najaf. “What happened to all the promises that were made?” said Raad Jaafar. “We don't want a leader who just gives guns to rich tribal sheikhs. Is this how Iraq wants to help the poor?” He said he would not vote for Maliki, who did well in provincial elections in January 2009, when he put security improvements at the center of his campaign. But out of 15 policemen interviewed at a Najaf polling center, most said they backed Maliki's State of Law coalition. Campaigning for a second term, Maliki has claimed credit for lower levels of violence as sectarian bloodletting between Sunnis and Shiites recedes. But a series of devastating suicide bombings in Baghdad has undercut the Shiite prime minister's security credentials.