Attacks targeting security forces across Iraq left three policemen and an army officer dead on Wednesday, officials said, amid a spike in unrest as the country grapples with a political crisis.

Two policemen were shot dead and three others were wounded by gunmen at a checkpoint in the town of Mussayib, south of Baghdad, while one police officer was killed and another hurt by gunfire in the main northern city of Mosul.

North of Baghdad in the town of Tuz Khurmatu, an army lieutenant colonel was killed and another officer was wounded by a roadside bomb while on patrol, officials said.

And in the capital, four people, including one policeman, were wounded by a roadside bomb targeting a police patrol.

No organisation has claimed responsibility for the deadly string of attacks, but Sunni militants including Al-Qaeda's front group often target security forces and government targets in a bid to destabilise the country and push it back to the sectarian war that blighted Iraq from 2005 to 2008.

The violence took the death toll since Sunday to 72, indicating a spike in attacks amid a political crisis pitting Prime Minister Nuri al-Maliki against his government partners as weeks of rallies have called for his ouster.