The US military said it dropped a 500lb laser-guided bomb on a house, mistaking it for a nearby suspected hideout of fighters. It said five people were killed.
An official from a joint US-Iraqi security centre for the Salahuddin province put the toll at 13, including four women and three children. He said the dead were all from the same family.
Reuters pictures showed a house in the village of Aaytha, southeast of the northern city of Mosul, reduced to rubble.
They also showed rows of freshly dug graves where locals said the dead had been buried.
Earlier a bomber killed four people near a checkpoint south of Baghdad, and anti-US fighters have abducted three senior Iraqi officials.
In the past week alone, fighters have killed nearly 100 people in bombings, ambushes and assassinations mostly targeting fledgling security services they regard as collaborators.
Under pressure to quell the violence, the US military said it had captured a key leader of a group headed by self-declared al-Qaida ally Abu Musab al-Zarqawi, responsible for some of the bloodiest attacks.
It said the arrest marked "significant progress in the inevitable destruction of the ... Zarqawi terrorist network" in the volatile northern city of Mosul.
George Bush says four of the 18
districts are too unstable to vote
South of Baghdad on Saturday, a car bomb tore through a petrol station in the village of Mahawil, killing four people and wounding 19 others who had been queuing at the fuel pump, police said.
The blast struck near a roadblock manned by police and soldiers.
Three Sunni officials from Saddam's hometown of Tikrit were abducted on a road south of Baghdad while returning from the Shia holy city of Najaf where they held talks with Shia leaders to bridge sectarian divisions over the elections.
The delegation included the head of the northern Salahuddin provincial council, the deputy to the provincial governor and the dean of Tikrit law school, police and tribal sources said.
Some Sunni leaders have called for a delay in the vote, saying persistent attacks in the Sunni heartland would scare away many voters and skew the results in favour of the Shia.
Some Sunni leaders have called
for the elections to be delayed
But interim Prime Minister Iyad Allawi has rejected any postponement of the vote.
In other violence on Saturday, armed men shot dead two Iraqi National Guards south of Samarra, and the bodies of three Iraqi contractors who worked with American forces were found near the northern city, security officials said.