The Islamic State (IS) group has now claimed responsibility for a suicide attack that has killed 15 people at a mosque in Saudi Arabia near the Yemeni border, according to state media.
The mosque, in the city of Abha in the southern Aseer province, served a state security unit called the Special Emergency Force, according to the state television channel al-Ekhbariya, reported the Guardian. All those killed were members, said the channel.
A suicide attack on a Shia mosque in May killed 21 people and injured more than 100 in Saudi Arabia's worst attack in a decade.
No one immediately claimed responsibility for the blast in the city of Abha, which is close to Saudi Arabia's southern border with war-torn Yemen.
An Interior Ministry statement said 13 were killed and that 10 of those killed were members of the security forces. Security officials later told the Associated Press that two more security personnel were confirmed dead, raising the death toll in the attack to 15.
Earlier, the state-owned Al-Ekhbariya news gave a higher death toll, reporting that 17 had been killed in the attack. It was not immediately clear why there was a discrepancy, but conflicting reports are common in the chaotic aftermath of bombings.
Interior Ministry spokesman Mansour al-Turki said initial findings point to the attack being carried out by a suicide bomber wearing an explosive vest.
A Saudi Interior Ministry official told the Associated Press that the bomb targeted police trainees as they were in the middle of prayer. All officials spoke on condition of anonymity because they were not authorized to speak to reporters. It was not immediately clear if the mosque was inside an Interior Ministry compound.
State TV carried images in the aftermath of the attack, which showed blood splattered on the walls and ceiling of the mosque, alongside debris.
Thursday's attack was the deadliest against Saudi security forces since IS attacks first appeared in the kingdom last year. Saudi Interior Minister and Crown Prince Mohammed bin Nayef cut short a visit to Egypt, where he was to attend the inauguration of an extension of the Suez Canal, to return to Saudi Arabia following news of the attack, officials said.
In May, a suicide bomber struck a Shiite mosque in the eastern village of al-Qudeeh, killing 22 people. That was the deadliest militant assault in the kingdom in more than a decade, and was followed a week later by another suicide bombing outside another eastern Shiite mosque that left four dead.
Both those attacks were claimed by an IS affiliate fighting in Iraq and Syria. Also, in November, a gunman opened fire at a mosque in the eastern Saudi village of al-Ahsa, killing eight people.
Saudi authorities last month announced the arrest of more than 400 suspects in an anti-terrorism sweep. They said at the time that they had thwarted other IS attacks being plotted in the oil-rich kingdom, including a suicide bomb plot targeting a large mosque in eastern Saudi Arabia that can hold 3,000 worshippers, and attempts to attack other mosques, diplomatic missions, and security bodies.
Saudi Arabia is also leading a coalition targeting Iran-allied Shiite rebels in neighboring Yemen, not far from Abha. The rebels have carried out a number of cross-border attacks against military targets.
The Associated Press contributed to this report