capital city of Tikrit, a provincial police source said.

In a separate incident, a government-backed Sahwa paramilitary group was shot dead by gunmen outside a polling center at Albu- Ajil area, just east of Tikrit, some 170 km north of Baghdad, the source said.

Three more policemen were wounded in a roadside bomb explosion at a polling center in the town of Siniyah, some 40 km north of Tikrit, the source said, adding that traffic ban across the province was imposed after the attacks.

In northern Iraq, the guards opened fire on two suicide bombers who tried to break into a polling center in central city of Mosul, some 400 km north of Baghdad, killing one of them. The other one blew up his vest, wounding five policemen, a local policesource said.

In Anbar province, two policemen were killed and five others wounded in a roadside bomb explosion at a polling center in the town of Habaniyah, some 80 km west of Baghdad, a provincial police source told Xinhua.

Over one million voters from the security personnel, inmates, patients cast their ballots in 532 polling centers in some schools, prisons and hospitals across the 18 provinces of the country ahead of Iraq's landmark elections to choose next lawmakers.

More than 9,000 candidates from nearly 280 political entities are vying for the 328 parliamentary seats in Iraq's April 30 general election, the first since the withdrawal of U.S. troops from the country at the end of 2011.