At least 15 people, most of them members of the Saudi special forces, were killed Thursday in a suicide bomb attack at a mosque used by the force in Saudi Arabia’s Abha city, according to the country’s interior ministry.

An interior ministry spokesman told state news agency SPA that “the mosque in Abha, the capital of Asir province, was part of the local headquarters of the Special Emergency Force,” revealed Reuters.

Earlier, the ministry reportedly gave a slightly lower toll of “more than 13 dead and 22 others injured,” but later revealed that two of the wounded had perished.

Some news agencies have reported that as many as 17 people were killed in the attack.

State-run TV channel El-Ikhbariya mentioned that the assault occurred during the time of prayer, Al Arabiya News Channel reported.

Quoting an interior ministry spokesman, Reuters revealed that “men were praying in the mosque when the bomber struck within their ranks,” adding that “the debris of the blast appeared to show an explosive belt had been used.”

“Saudi Arabia is treating the incident as a terror attack,” noted International Business Times (IBT).

Citing the interior ministry, Reuters reported that of the estimated 15 fatalities, “12 were members of the [Special Emergency Force], while three were workers in the compound.”

No one has claimed responsibility for the attack, BBC reported, quoting officials.

The death toll is expected to rise due to the number of people who were critically wounded, pointed out Middle East Eye.

A source in the kingdom told Middle East Eye, on condition of anonymity, that “the bomber was disguised as a cleaner in order to gain access to the mosque and once inside detonated a suicide belt among the security forces who were praying at the time.”

The city of Abha, where the attack took place, is located in southwest Saudi Arabia, near the country’s border with Yemen, where Saudi Arabia is leading a coalition against Iran-backed Shiite Houthi rebels.

The Islamic State (ISIS/ISIL) claimed responsibility for two suicide bomb attacks in May on Shiite mosques in Saudi Arabia that ended up killing at least 25 worshippers and wounding dozens.

ISIS is “bitterly opposed to Gulf Arab rulers” and “is trying to stir sectarian confrontation on the Arabian peninsula to bring about the overthrow of the states’ ruling dynasties,” Reuters noted.

“It has urged young Saudi Sunnis in the kingdom to attack targets including Shi’ites,” it added. “There was no immediate indication of the sectarian affiliation of the mosque in Thursday’s bombing.”

Thursday’s suicide attack comes at time when Saudi Arabia is cracking down on ISIS supporters in the country.

In July, the kingdom claimed it had arrested 431 suspected members of ISIS in the course of several weeks.