The blast tore through a crowd waiting to apply for jobs in the force on Saturday, according to National Guard General Anwar Muhammad Amin.
At least 53 people were wounded, some of whom are in critical condition, doctors at Kirkuk hospital said. The bomber detonated his car at the rear entrance of the National Guard headquarters in a residential area of the city.
The street outside the national guard building was littered with bloodied bodies, debris and shards of glass.
Saturday's attack was the third car bombing against Iraq's beleaguered police forces this week.
On Friday, an attacker rammed an explosives-packed vehicle into a row of police cars in the capital, killing at least three, days after a car bomb near a Baghdad police station left at least 44 dead.
Meanwhile, in Baquba, north of Baghdad, nine people were wounded after a mortar shell struck a crowd of students and parents awaiting exam results in front of a school.
"A mortar shell exploded near the secretary's office, wounding several people," said local police chief General Walid Khalid Abd Al-Salam on Saturday.
Hospital officials said the injured
in Baquba had shrapnel wounds
Hospital officials said nine people had been brought in with shrapnel wounds.
The city, north of Baghdad, has seen several attacks against Iraqi security forces and US troops.
On 14 September, 12 Iraqi policemen and their driver were killed in Baquba when gunmen sprayed their vehicle with bullets.
Earlier in Baghdad, on Saturday, a roadside bomb exploded in a small sidestreet in the city centre, killing one man and seriously wounding two in a passing car, police and witnesses said.
Residents identified the three men as Iraqis who worked as security guards at the nearby al-Sadir Hotel, a heavily fortified complex where US civilian contractors and other Westerners involved in Iraq's reconstruction effort are known to live and work.
The three men were wearing uniforms, body armour and carrying assault rifles, according to the witnesses.
Meanwhile, west of Baghdad, residents found the body of Anbar province's deputy governor, who was kidnapped earlier this month, hospital officials said on Saturday.
Basim Muhammad's body was found on Friday evening near Ramadi General Hospital, said Dr Abd Al-Munaim Aftan, the facility's director.
Also close to Baghdad, three Iraqi children were seriously injured after US forces opened fire at them. They were throwing stones at the soldiers in the Abu Ghraib area west of Baghdad on Saturday.
In Basra, a member of Shia cleric Muqtada al-Sadr's Al-Mahdi Army has been killed during clashes with British forces in al-Twaisa area.
A British soldier was seriously injured after Al-Mahdi Army fighters opened fire at a patrol in the city, Captain Hisham Halawi, a spokesman for the British forces, told Aljazeera.
In Baghdad a blast killed one
person and injured two others
In the southern city of Mosul, an explosive device detonated as a US military patrol passed through the area. One military vehicle was damaged.
US troops hit
A US convoy was hit by a roadside bomb on the main highway to the airport in southern Baghdad and another convoy was targeted by a car bomb moments later, witnesses said.
The double attack took place shortly after 1200 GMT. Two vehicles were seen on fire, apparently an explosives-laden civilian car and a US Humvee all-terrain vehicle which it rammed.
The ramming took place on a fly-over. Black smoke was billowing in the sky and US troops sealed off the area. There was no immediate comment from the US military.