Three people were killed and 13 wounded when a roadside bomb hit a minibus in the sprawling Baghdad Shiite neighbourhood of Sadr City on Monday, security officials said.
Hospital officials said that the three dead and 12 of the wounded were university students on their way to take their final exams, while the other casualty was the minibus driver.
It was the latest bloody bombing in the runup to the planned pullout of US troops from Iraqi towns and cities by June 30.
Violence has dropped markedly in Iraq in recent months, with May seeing the lowest Iraqi death toll since the 2003 invasion.
But attacks remain common, particularly in Baghdad and the main northern city of Mosul.