A policeman at the scene said a pick-up truck had pulled up to the checkpoint and detonated seconds later.
A cameraman working for Reuters who was at the scene shortly after the blast on Tuesday said it caused widespread destruction.
"There are still bodies lying in the street," he said.
Doctors said two bodies and nine wounded people had been brought in to the local hospital.
The explosion occurred in the Kanaan area of Baquba, a city about 65km north of Baghdad that has seen frequent outbreaks of violence.