Police spokesperson Colonel Mohammed al-Harbi said that a man in the Abu Arish area of Jazan region, bordering Yemen, reported at about 2:30 am that his father "was being shot at from an unknown source at his farm".
Police did not identify the victim or give further details of his former security duties.
Gunmen kill two Saudi policemen: polic
They said a "criminal investigation" was under way into the killing. Usually the Saudi authorities describe IS-related attacks as "terrorism".
IS said in a statement that it had shot dead retired Brigadier Ahmed Fayie Assiri "at his farm in Abu Arish area of Jazan."
IS has claimed previous attacks on Saudi security forces as well as deadly bombings and shootings that targeted the Sunni kingdom's Shia minority, which the Sunni militant IS group considers to be heretics.
Jazan and other southern border districts have also been subjected to shelling from Yemen since last March when Saudi Arabia began leading an Arab military coalition against Houthi rebels in the neighbouring country.
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