The soldiers had not been called to the scene by officials or police, but decided to intervene after passing by during regular patrols, according to Mamman.
Police had tried to pacify the students before the soldiers arrived but "all frantic efforts to get them off the highway failed," he said.
"In the course of their normal patrol (a military unit) saw the chaos on the federal highway and decided to clear the road. Students began to throw pebbles and it led to some shooting. Some students were wounded," he continued.
He added that while he had heard reports of deaths, he could not confirm that those killed were students.
The university has been closed indefinitely, the registrar said.
Nigeria's security forces have repeatedly been accused of using excessive force, including to stamp out protests.
- AFP