BAGHDAD: The toll from a wave of attacks in Iraq mainly targeting security forces and Shiites rose on Friday to 51 killed, 26 of them police and soldiers, security officials and doctors said.

Thursday's attacks came amid a surge in violence that has killed more than 2,500 people already this year, including upwards of 250 so far this month.

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

In Thursday's single deadliest incident, gunmen shot dead 11 police charged with protecting the country's vital oil infrastructure and three soldiers on the road between Haditha and Baiji, northwest of the Iraqi capital.

In another 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.

And a car bomb near a Shiite religious hall close to Dujail, north of Baghdad, killed nine people and wounded 21 more. Many people gather at places of worship at night during the Muslim holy month of Ramadan, which began earlier this week. Sunni militants including those linked to Al-Qaeda frequently target members of Iraq's 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.

Security forces are also frequently targeted in attacks.

Violence in Iraq has declined from its peak at the height of the sectarian conflict in 2006 and 2007, but the number of deaths in attacks have been on the rise since the beginning of 2013.