Two Iraqi soldiers and two civilians were also wounded in the attack in Baghdad's Karrada district.
The bomb hit the convoy which was passing by the National Theatre at about 10am [0700GMT].
The assailants are unknown.
'Rising stakes'

Al Jazeera's Owen Fay in Baghdad said: "Authorities are trying to determine whether she was the target of this attack or whether the convoy simply got unlucky, drove into an area they shouldn't have and struck an IED that was buried in the road


"That is obviously the focal point of the investigation at this stage.


"Nobody has claimed responsibility and the government is mulling its reaction at the moment.


"There is an investigation into this and if it does turn out that the president's wife or the families of any senior politicians in this country are now being targeted directly then that raises the stakes significantly."

Iraq has seen a large increase in violence in the past month, in the main between Shia militias loyal to Muqtada al-Sadr and US and government forces.