US and Iraqi forces have poured thousands of extra troops into Baghdad over the past two months in an attempt to halt Iraq's slide into all-out sectarian civil war.
Mohammed El-Waqa'a, a police brigadier general, said: "Workers were travelling back from a textile plant in Mosul to their home in Bashika, east of the city. Several gunmen stopped the buses, chose the Yezidi among the passengers and killed them in front of everybody."
While the increase in troop levels has reduced killings by sectarian death squads, car bomb attacks still plague Baghdad.
A wave of car bombs killed nearly 200 people in the coty last Wednesday, the worst violence in the capital since the security plan began.
General David Petraeus, the US commander in Iraq, said in remarks published on Sunday that the troop build-up had yielded modest progress but a rise in suicide bombings made the ultimate success of the security crackdown uncertain.
Petraeus and other senior US officers in Iraq told The Washington Post in interviews that the increase in US and Iraqi troops had improved security in Baghdad and the Anbar province to the west, but that attacks had risen sharply in other regions.
They said it was critical for Iraqi leaders to make the political compromises needed to ensure long-term stability.
"The chances of success [in Iraq] are essentially zero because the Iraqi people have no voice"
Non Sequitur, Cadiz, Spain
Send us your viewsGeorge Bush, the US president, has committed almost 30,000 additional troops mostly to Baghdad, the centre of Iraq's sectarian violence.
The military commanders told the Post that sectarian killings in Baghdad fell to fewer than 400 in March from 1,200 in January.
Petraeus was quoted as saying: "We have certainly pulled neighbourhoods back from the brink."
But the commanders said the increase in suicide bomb attacks was troubling because of the danger of reigniting sectarian revenge killings and undermining the government of Nuri al-Maliki, Iraq's prime minister.
Petraeus said: "I don't think you're ever going to get rid of all the car bombs. Iraq is going to have to learn - as did, say, Northern Ireland, to live with some degree of sensational attacks."
He said a more realistic goal was preventing the bombings from causing "horrific damage".
Two American soldiers were killed in attacks in Baghdad on Saturday, the US military said. One was killed by small arms fire while another died in a roadside bomb blast. Another soldier was killed southwest of the capital.
At least 70 US soldiers have been killed this month, putting April on course to be the deadliest month for American forces in Iraq this year. More than 3,300 US soldiers have been reported killed since the US-led invasion of Iraq in 2003.