A suicide bomber has blown himself up in a mosque inside a local security force headquarters in Abha, the capital of Saudi Arabia's south western province of Asseer.
According to an interior ministry spokesman quoted on Saudi state TV, 13 people were killed and nine people were wounded in the attack near the Yemeni border.
Interior Ministry spokesman Major General Mansour al-Turki said initial findings point to the attack being carried out by a suicide bomber in an explosive vest.
State television had earlier reported at least 17 people were dead.
The mosque was principally for a state security unit called the Special Emergency Force and 10 members are believed to have been killed, the TV channel reported.
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Another interior ministry official told AP that the bomb targeted police trainees while they were in prayer.
The three other victims were workers in the compound.
No terrorist group has yet claimed responsibility for the attack but last month Saudi forces arrested over 400 suspected members of Isis who were alledged to be plotting attacks on police and mosques in the country.
An Isis suicide bomber stuck a Shiite mosque in the eastern village of al-Ahsa in May and killed 22 people. A week later, another bomb attack outside another eastern Shiite mosque killed four.
More to follow
Additional reporting by Reuters and AP
