The latest bombing came as the Sunni Muslim worshippers were leaving the Saad Ibn Abi Wakkas mosque in Khalis, 80km from the capital, after Friday prayers.
Another Sunni Muslim, in the southern port city of Basra, was shot dead by unidentified men, also on leaving a mosque after prayers.
Sectarian violence has been on the rise in Iraq since February 22 when a bomb destroyed a revered Shia shrine in Samarra, north of the capital. Hundreds have since been murdered in tit-for-tat killings.
In Baghdad, where bodies are now found on a daily basis, 15 corpses were picked up on Friday, 12 in the east and northeast of the city, and three in the west, an Interior Mministry official said. They had been tortured and shot.
In the week of March 11 to 17, US forces tracked 58 such incidents, involving 134 dead, in the capital alone, according to US Major-General Rick Lynch, who described the killings as "ethnic-sectarian".
In other violence on Friday, seven people, three of them policemen, were killed in the capital.
Armed men raided a baker's shop in the south of the capital, shooting dead four employees and wounding a fifth. When police arrived on the scene, a roadside bomb exploded, killing one police officer and wounding another.
Assailants also ambushed police in the west of the city, shooting dead two and wounding one.
Iraqi Shia worshippers protest on
Thursday after a deadly attack
Two US soldiers were killed in combat in Iraq's Anbar province, the US military reported on Friday. The statement said the soldiers, assigned to the 2/28th Brigade Combat Team, were killed on Thursday.
Their names were withheld until relatives were notified. The deaths raised to at least 2320 the number of US military personnel who have died since the beginning of the Iraq war in March 2003, according to an Associated Press count.
In Copenhagen, the Danish military announced that a Danish soldier had been killed and another slightly wounded on Thursday by a bomb attack on their patrol near the town of Al Harta in southern Iraq.
This was the third killing of a Danish soldier in Iraq since August 2003.
Iraq's president issued a highly optimistic report on Friday on progress among politicians trying to hammer out the shape of a new unity governmen.
Jalal Talabani said the government could be in place for parliamentary approval by the end of the month, but acknowledged "I am usually a very optimistic person".
He spoke to reporters after a fifth round of multi-party talks among the country's highly polaris ed political factions.
Iraqi police recruits are a regular
target of attack by fighters
Talabani said politicians had agreed on Friday to a method for choosing the government.
Fellow Kurdish politician Mahmoud Othman said the high-level talks resumed and took up a 28-point political statement that would outline the programme of any new government, once formed.
Another negotiating session was set for Saturday, he said.
The political talks resumed as some among the politicians floated suggestions that the Shia bloc would seek a way out of the impasse over Ibrahim al-Jafaari, the prime minister, by naming three candidates for the premiership, politicians and officials close to the talks said on Thursday, on condition of anonymity because of the sensitive juncture in the negotiations.
Among the names suggested for the post is that of Qassim Dawoud, a former national security adviser. Dawoud told The Associated Press, however, he had not heard such a suggestion.
In the capital, British peace activist Norman Kember, 74, held hostage for four months by Iraqi kidnappers, began his journey home on Friday when he boarded a British military transport, said Christian Peacemakers Teams spokeswoman Peggy Gish said.
Fellow hostages Harmeet Singh Sooden, 33, and James Loney, 41, Canadians kidnapped with Kember, would be leaving the country this weekend.