A grenade exploded in the camp of 17 Punjab unit of the army posted at Trehgam in Kupwara district, 100km from here, the sources said.
They said four jawans were critically injured in the explosion and were shifted to hospital at the headquarters of the 15 Corps of the army here.
The sources said it was not immediately clear how the explosion took place.
Defence spokesman Lt Colonel J S Brar refused to comment on the incident.