Militants killed 25 Iraqi security forces members in a wave of attacks on Thursday, and 15 people died in other attacks, including 10 in twin bombings targeting mourners, officials said.

The latest attacks come as Iraq witnesses a surge in violence that has killed more than 2,500 people already this year, including upwards of 240 so far this month.

Analysts point to widespread discontent among the minority Sunni community, and the failure of the Shiite authorities to address their grievances, as the main factors driving the rise in violence.

In the single deadliest attack, gunmen shot dead 14 members of the security forces, including 11 charged with protecting the country's vital oil infrastructure, on the road between Haditha and Baiji, northwest of the Iraqi capital.

In another bloody attack, a car bomb ripped through a funeral tent where family members of a Shiite man were receiving condolences in Muqdadiyah, northeast of Baghdad, and a suicide bomber detonated explosives when emergency personnel arrived.

The blasts killed a total of 10 people and wounded 22.

Sunni militants including those linked to Al-Qaeda frequently target members of the Shiite majority, whom they regard as apostates.

Iraq was plagued by sectarian violence that killed tens of thousands of people in past years, and there are persistent fears that tensions will again boil over into all-out conflict.

In Tikrit, north of Baghdad, three roadside bombs targeted police patrols, killing three policemen and wounding five.

And in Khaldiya in Anbar province, militants opened fire on a police station, after which one suicide bomber detonated an explosives belt in the station, and another blew up an explosives-rigged car, killing four police and wounding eight.

One attacker was shot dead during the assault.

Militants also fired three mortar rounds at the police directorate in Fallujah, also in Anbar, after which a suicide car bomber struck near the building and clashes erupted.

One policeman was killed and three were wounded in the violence.

Those attacks came after a suicide bomber detonated an explosives-rigged vehicle near a convoy on a highway in Anbar on Wednesday night, killing two policemen and wounding two others.

A car bomb also rocked south-central Baghdad on Thursday, killing one policeman and two civilians, and wounding nine.

The blast shook windows and sent a massive cloud of smoke billowing into the sky over the capital.

Fire trucks, ambulances and security forces in white pickups with machineguns mounted in the beds raced to the scene.

In the northern city of Mosul, gunmen killed a soldier in front of his home, and a roadside bomb killed a policeman and wounded another.

Another man was shot dead south of Mosul, while gunmen killed a man in the Sharqat area, northwest of Baghdad.

And in the northern town of Tuz Khurmatu, a car bomb wounded 32 people, while two other car bombs northwest of the city of Kirkuk wounded 14.

Both areas are part of a swathe of north Iraq territory that the autonomous Kurdistan region wants to incorporate over the strong objections of the federal government in Baghdad -- a dispute that diplomats and officials say is one of the most serious long-term threats to Iraq's stability.