A suicide bomber targeting a mosque used by Saudi police has killed at least 17 people in the southern city of Abha, state television El-Ikhbariya reports.
The explosion took place as worshippers were praying at a mosque used by Saudi special forces in Aseer province, the broadcaster said, describing it as a "terrorist" attack.
An interior ministry spokesman confirmed the attack but gave a slightly lower toll of "more than 13" dead.
The victims were members of a Special Weapons and Tactics (SWAT) unit, the spokesman said.
"It's confirmed there's an explosion and there's more than 13 (killed)... in a mosque," the spokesman said.
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The explosion happened at the headquarters of the SWAT team, which is tasked with domestic security, he added.
It was too early to say who may have carried out the attack, he added.
The attack is the latest in a spate of bombings in the country, many targeting members of the Shi'ite minority.
