An Iranian soldier opened fire on his colleagues, killing five, at an army base near Kerman in the southeast of the country, Iranian media reported on Sunday evening.
Brigadier General Amir Gholamalian told Iranian media that on Sunday afternoon, "one of our soldiers, who was guarding the unit, entered the soldier's infirmary and shot his comrades.
"The motive is still unknown," Gholamalian said.
"Unfortunately, as a result of this shooting, five of this soldier's comrades lost their lives," he added.
Kerman was recently the site of two explosions on January 3, as gatherers were marking four years since the assassination of Islamic Revolutionary Guards Corps general Qasem Soleimani.
Some 94 people were killed in the attack, carried out by two Tajiki suicide bombers in the name of ISIS.