Riyadh, Asharq Al-Awsat—A deadly attack on Saudi border guards along the Saudi-Iraqi frontier this week was carried out by Saudi members of the Islamic State of Iraq and Syria (ISIS) seeking to cross back into the Kingdom undetected, security sources told Asharq Al-Awsat.

This comes as the Saudi Interior Ministry confirmed that at least three of the four attackers were Saudi nationals. The identities of the three Saudi attackers have been revealed as Mamdouh Al-Mutairi, Abdulrahman Al-Shamrani and Abdullah Al-Shammari. The identity of a fourth attacker, who detonated an explosive belt after being captured, remains unknown.

The attack resulted in the deaths of three Saudi border guards, including commanding officer Gen. Oudah Al-Belawi, and all four attackers. The four men were seeking to infiltrate Saudi territory from Iraq on Monday and were confronted by Saudi border guards close to Arar, capital of the Northern Borders Province.

In comments to Asharq Al-Awsat, Interior Ministry spokesman Maj. Gen. Mansour Al-Turki said that the three Saudi nationals left the Kingdom separately in 2013 and that Mutairi was previously arrested for having ties to Al-Qaeda but was released on bail.

Turki also revealed that Abdullah Al-Shammari was the brother of Mutlaq Al-Shammari, a terrorist killed in an exchange of fire with security forces in Mecca in 2006.

Security forces seized automatic weapons, hand grenades and explosive belts, including Iraqi and Syrian bank notes, at the scene of the attack.

The Saudi Interior Ministry on Friday announced that three Saudi nationals and four Syrian nationals had been arrested in Arar in connection with the attack.

“Security investigations with the seven suspects will uncover whether they had any intention to carry out terrorist operations, as well as any other people who might have connections to the attackers,” Turki said.

“At this time, we cannot rule out if they were going to aid and assist the attackers to infiltrate Arar,” he added.

Security sources, speaking to Asharq Al-Awsat on the condition of anonymity, said that the seven suspects were arrested following information obtained from cell phones that the attackers had been carrying.

The sources also claimed that both Mutairi and Shammari were on the Saudi no-fly list but had managed to sneak out of the country illegally, making their way to Syria where they joined ISIS.

Investigations into the deadly attack, and any ties that the attackers have inside and outside the Kingdom, are ongoing, Turki said.

The official Saudi Press Agency, quoting an Interior Ministry spokesman, confirmed that the attackers were members of the “deviant” group. Official statements have traditionally described Al-Qaeda in such terms, although Riyadh has since expanded the expression to include ISIS.