Images of the incident showed the completely mangled front end of a white bus, with blood-flecked seats, personal items and a shoe strewn around the tree-lined crash site.
"In view of this tragedy, the head of state extends his deepest condolences to the families of the victims and wishes a speedy recovery to the injured," the government statement said.
Public prosecutor, Cheikh Dieng, said in a statement that early investigations suggested a public passenger bus suffered a burst tire and swerved off course.
It then crashed "head-on with another bus coming in the opposite direction", he said.
Colonel Cheikh Fall, who heads operations for the National Fire Brigade, told AFP the victims were taken to a hospital and medical center in Kaffrine.