In one incident, four Iraqi police officers and five police trainees were killed on Tuesday in a drive-by shooting as they headed to work south of Baghdad.
They were fired upon by attackers shooting from their cars, police said.
Reuters Television footage showed a yellow minibus riddled with bullet holes, the seats splattered with blood.
"They were killed at around 7.30 this morning (0430 GMT)," Mussayab police chief Major Kadhim Ajmi said.
"They were shot by unknown attackers driving a red Opel."
Local officials said the minibus was attacked shortly after leaving the town of Mussayab on its way to Hilla, about 100 km south of Baghdad. Staff at Mussayab General Hospital said three other passengers were wounded.
In the other incident also on Tuesday, two policemen were killed in a drive-by shooting, near the northern city of Kirkuk.
Ali Kadhim, 26, and his 23-year-old brother were shot dead at a checkpoint in the centre of the city, said Colonel Muness Ishak.
"The attack was carried out when four men in a white car drove past the checkpoint and opened fire with machine guns..."
Colonel Muness Ishak,
Two of their colleagues were seriously wounded, one of them losing an eye.
"The attack was carried out when four men in a white car drove past the checkpoint and opened fire with machine guns, killing two policemen and injuring two others," Ishak said.
Police have often been attacked by fighters who accuse them of cooperating too closely with the US-led occupiers.
There have been several drive-by shootings in the Hilla area of Kirkuk in recent weeks, and drive-by attacks have been on the increase throughout the country.
On 16 March fighters ambushed and killed a Dutch and a German engineer near Mussayab. The week before that, two US civilians from the defence department and their Iraqi translator were shot dead on another road nearby.
Earlier, two rockets were fired at Kirkuk airport, which houses a key US military base in the region.
The attack occurred at midnight (21:00 GMT) and huge columns of smoke were seen rising from the base, the city's police chief, General Turhan Yusuf, said without elaborating.