The claims by the so-called Hijaz Province of the Islamic State appeared hours after today's attack in the city of Abha, close to Saudi Arabia's southern border with war-torn Yemen.
It was carried on IS-affiliated Twitter accounts and was also reported by the SITE Intelligence Group, which tracks militant messages.
The statement says an IS suicide bomber targeted a "monument of the apostate".
It was the first claim by the purportedly new IS branch. Hijaz is a reference to the historic western part of Saudi Arabia that is home to Islam's holiest sites of Mecca Medina.