"At around 3pm [15:00] on Sunday gunshots were heard and a decision was taken to investigate their source," said spokesperson Musa Mntambo in a statement.
The field rangers closed all exits at the reserve while investigating the source of the gunshots.
Two men, one carrying a rifle, were confronted.
Mntambo said the armed man pointed his weapon at the rangers, who took cover and returned fire before the gunman could pull the trigger.
The gunman died and the second man fled.
Mntambo said police and other authorities launched a search for the second man.
He was one of three occupants found in a car driving toward Ulundi.
"During the interrogation that followed, one occupant admitted that he was with the suspect who had been shot earlier by the field rangers," he said.
All three men were arrested.