Saudi Interior ministry has said that 13 people were killed in a suicide attack on a mosque in the country's southwest region bordering Yemen.
The Interior Ministry's statement said 10 of those killed in the attack on Thursday in the city of Abha in Asir province were members of the security forces.
The attack on the mosque belonging to the emergency forces also injured at least nine others, the ministry added.
Earlier, state media said 17 people were killed.
Saudi Television said initial information indicated that the blast occurred after a suicide bomber detonated his explosive belt.
It was too early to say who may have carried out the attack, an interior ministry spokesman told AFP news agency.
There was also no immediate claim of responsibility, but groups affiliated with the Islamic State of Iraq and the Levant (ISIL) have been blamed for recent attacks in Saudi.
Jamal Khashoggi, a Saudi political analyst, said that if the latest attack is proven to be the handiwork of ISIL groups, it would be the largest ISIL attack targeting security forces inside Saudi.
"Those guys, they are at war with us," he told Al Jazeera. "This is shaking us to the ground."
Thursday'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 ISIL 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.
A group affiliated with ISIL 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 Shia mosque in Kuwait in June.
Source: Al Jazeera and agencies
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