BAGHDAD (AFP) - Gunmen killed 12 policemen and soldiers while a truck bomb hit a port in Iraq on Saturday, the latest in a surge in violence that the authorities have failed to curb.

Security forces have in recent weeks carried out some of their biggest operations since the 2011 withdrawal of US forces, but analysts and diplomats have said the authorities have not addressed the root causes of the violence.

Prime Minister Nuri al-Maliki has nevertheless vowed to press on with the campaign in a bid to combat Iraq's worst violence since 2008, and on Saturday the Interior Ministry's spokesman announced the killing of an alleged senior Al-Qaeda-linked militant.

In Saturday's deadliest attack, gunmen opened fire on an army post in the town of Madain, just south-east of Baghdad, in a pre-dawn attack that left five soldiers dead and three others wounded, police and a medical source said.

Among the dead was a lieutenant-colonel. The gunmen fled the scene after the attack, and security forces, who cordoned off the scene, launched a manhunt.

North of Baghdad, militants shot dead four police who were buying ice near the city of Tikrit.

Security forces often purchase large blocks of ice to distribute to nearby checkpoints in order to cope with Iraq's sweltering summer heat.

In another attack north of the capital, gunmen killed three soldiers in the restive Muqdadiyah area of Diyala province.

And in the far south, a truck rigged with explosives blew up in the parking lot of the port of Umm Qasr, wounding three people and damaging a docked ship and several nearby trucks.

No group immediately claimed responsibility for the attacks, but Sunni militants linked to Al-Qaeda and opposed to the Shi'ite-led government frequently carry out attacks against security forces.

Attacks have killed more than 3,480 people since the beginning of 2013, according to figures compiled by AFP.

Analysts and diplomats attribute the increased violence to anger in the Sunni Arab community over its alleged ill treatment at the hands of the Shi'ite-led authorities.

Security forces have been carrying out wide-ranging operations in multiple provinces including Baghdad, after brazen July assaults on two prisons, claimed by an Al-Qaeda front group.

Mr Maliki has said more than 800 alleged militants have been arrested and dozens killed in the operations.

Interior Ministry spokesman Saad Maan said on Saturday that security forces had killed a top Al-Qaeda militant in Tikrit and detained two of his aides.

He did not identify the man killed.