The jawan, who was arrested soon after the incident, fired at his colleagues at the 42 Rashtriya Rifles camp at Bijbehara, 45 kms from here, an Army spokesman said.
A junior commissioned officer (JCO) and three jawans were killed while another jawan was injured in the incident, the spokesman said.
The spokesman did not divulge the name of the arrested jawan or his victims. He said an investigation has been launched to ascertain the circumstances which led the jawan to open fire.
Senior army officials have rushed to the spot. This is the first incident of fratricide in the Army in the Valley in the past nearly two years.