An explosion probably triggered by a suicide bomber ripped through a mosque used by Saudi police today killing at least 13 people in the southern city of Abha, the interior ministry said.
A spokesman for the ministry, in a statement carried by the official Saudi Press Agency, said nine other people were wounded, three of them in serious condition.
He identified three of those killed as "workers" in a mosque used by members of a Special Weapons and Tactics (SWAT) domestic security unit in Abha, in the southern province of Asir.
"The terrorist attack struck worshippers during prayer. Ten policemen and three workers were killed while nine were wounded, three seriously," the spokesman said.
He said the attack was likely carried out by a suicide bomber, saying that "body parts found at the scene" indicated the use of explosive vests.
State television El-Ikhbariya, which broke the news earlier, gave a death toll of 17.
It was too early to say who may have carried out the attack, an interior ministry spokesman told AFP.
There was no immediate claim of responsibility.
Today's bombing was the most serious in recent months against Saudi security forces, who have been targeted in attacks blamed on the Islamic State group.
In mid-July, a car bomb exploded at a security checkpoint near a prison in the capital Riyadh. It killed the 19-year-old driver and wounded two policemen, the interior ministry said.
In the southwestern city of Taif on July 3, a policeman was gunned down during a raid in which three people were arrested and flags of the IS group found, police said earlier.
On successive Fridays in May suicide bombings at mosques of the minority Shiite community in Eastern Province killed a total of 25 people.
An IS-affiliated group calling itself Najd Province -- which takes its name from the region around Riyadh -- claimed those attacks as well as another suicide bombing that killed 26 people at a Shiite mosque in Kuwait in June.
The group considers Shiites to be heretics.
