Police and bodyguards in the convoy opened fire after the blast. Several vehicles crashed and others sped away.
Haidar Jamal, an Iraqi journalist, told Al Jazeera: "The explosion took place in Bab Sharji neighbourhood, a few metres away from the Green Zone. Only the Jadiriya bridge links these two areas, and that is why Bab Sharji is mostly frequented by officials heading towards the Green Zone."
Violence across Iraq has fallen over the past year to four-year lows, but fighters are still able to carry out frequent car bomb and suicide bomb attacks.
Suicide bombings are a signature tactic of al-Qaeda in Iraq.