Residents said about 50 gunmen were involved in the attack on Nahrawan, south east of Baghdad.
Many of the dead were Shia migrant workers gunned down by suspected al-Qaeda fighters in a dusk raid at a brick works.
Police said others were killed at a local power plant.
A local politician put the toll as high as 25, including a woman and three children, including six year old girl.
“They all have a single bullet to the forehead,” municipal council leader Alaa Abdul-Sahib al-Lamy told Reuters.
“I’ve sat here … where the bodies were brought and wept all morning.”
At least 500 people have died since a holy Shia shrine was bombed last week in the city of Samarra.
A daytime curfew was in force in the capital during Friday prayers, in an attempt to curb a surge in violence.
Iraqi police and troops, some in Soviet-built tanks, blocked deserted streets, as US forces kept a low profile.
Hopes of a withdrawal of US troops have been in the balance as armed groups on both sides made preparations for civil war.
Embattled Shi’ite Prime Minister Ibrahim al-Jaafari warned against “inflammatory” sermons.
Many worshippers heard calls for Muslim unity after the bombing of a Shi’ite mosque on February 22.
Mr Jaafari and US officials have blamed al Qaeda for the bombing of the Golden Mosque in Samarra.
He rallied Sunni and other leaders into resuming talks on a US-sponsored unity government to help stem the violence.
Officials agreed parliament should meet within 10 days or so.
But potential partners kept up pressure on the dominant Shi’ites to ditch Jaafari as their price for joining a coalition.
There have been signs some Shi’ites may now turn on the premier.
After an ill-tempered meeting of Mr Jaafari’s Alliance bloc, political sources said some rival Shi’ite factions were considering rerunning an internal ballot, which Jaafari won last month by a single vote to hold on to his job.
“We have reservations on Jaafari as prime minister,” Sunni Accordance Front spokesman Zafir al-Ani said.
The Sunni bloc had written to Alliance leaders urging a change of premier, he said.
“They have no choice”, one Sunni politician said, if the Shi’ites wanted Sunnis to join a coalition.
As the biggest party in parliament, the Alliance nominates the prime minister.
Despite the wrangling, parliament will convene for the first time since December’s election around March 12, satisfying a constitutional requirement, government sources said.
But political sources said they no longer expected that session to coincide with an allocation of posts, including the presidency and ministerial portfolios.
At best, a speaker would be elected to chair the assembly for four years.
Critics accuse Mr Jaafari, a soft-spoken Islamist doctor, of failing to combat rebel violence and economic collapse in his year as interim prime minister.
US President George W Bush says a government of Shi’ites, Sunnis, Kurds and others could bring stability and let him start bringing home some of the 133,000 American soldiers now in Iraq.
Facing their gravest crisis since the US invasion of 2003, Mr Bush
said this week that the choice for Iraqis’ was between “chaos or unity”.
Mr Jaafari has ordered thousands of troops and police onto the streets of Baghdad, backed by US soldiers, but their effectiveness is untested and their loyalties are uncertain in the face of sectarian militias to which some once belonged.
Many Sunnis, dominant under Saddam Hussein and suspicious of the US-installed political system, view the police and army as hostile and under the control of Shi’ite and Kurdish interests.
At the Sunni Saadiya mosque in the west of the capital, protected by two police cars, about 150 worshippers heard praise from the pulpit for local Shi’ites who came to help defend the building against reprisal attacks after the Samarra bombing.
Abu Alaa, a 46-year-old Shi’ite who went to the Sunni mosque to pray, said: “This is a time when we need to stand united.”