Iraq’s interior ministry reported that the bomber rammed his car into a bus carrying government staff outside the oil ministry in Baghdad.
Most of dead were oil ministry workers but two others killed were policemen from the nearby police academy.
Earlier a suicide car bomber killed 13 elite Iraqi police officers in an attack on a commando unit in the capital.
Ten others were wounded in the attack on the commando patrol on an eastern Baghdad highway, that was claimed by Iraq’s al-Qaeda wing in an Internet statement.
“A lion brother of the martyrs’ brigade on Sunday launched a heroic attack on a convoy of apostate commandos,” said the message, which could not be immediately authenticated.
The bombing follows overnight clashes between US troops and Shi’ite militiamen loyal to cleric Moqtada Sadr in the eastern Baghdad district of Sadr City, in which eight militia fighters were killed and five wounded, according to police.
It is the first fighting of its kind since a rebellion by Sadr followers ended more than a year ago.
The clashes broke out when US troops entered the Sadr City district to try to arrest members of the Mehdi army.
A US spokesman would not confirm the nature of the operation but said US forces came under attack but suffered no casualties.
However a Sadr spokesman claims US soldiers fired randomly and civilians were killed.
Tensions have flared in Iraq after fighting last week between the Iraqi military and British troops in the southern city of Basra.
In other violence on Sunday, a suicide bomber killed himself and six other people when his motorbike exploded in the mainly Shi’ite city of Musayyib, around 60 kilometres south of Baghdad, with 19 people wounded, said police.
In nearby Hilla, a bomber on a bicycle blew himself up in a crowded vegetable market, killing four people, including a woman and a child, and wounding 48.
And in western Baghdad, gunmen held up an armoured finance ministry convoy, killing two guards and wounding nine before making off with $US850,000 ($A1.12 million) in cash.
The string of attacks comes three weeks before Iraq is due to hold a referendum on a new draft constitution.
The US military has said it expects a surge in violence in the coming weeks ahead of the October 15 poll.
Iraqis are divided over the document, which is supposed to unite them and lay the foundations for a stable future.
In Ramadi, west of Baghdad, more than 1,000 people marched in protest over the constitution, which they say will divide Iraq along sectarian lines by giving too much autonomy to Kurds in the north and pro-Iranian Shi’ites in the south.
Tensions will also be running high as the referendum will be held four days before former dictator Saddam Hussein is due in court.
He faces charges of crimes against humanity in connection with the deaths of around 150 Shi’ite men following a failed assassination in 1982.