Riyadh, Asharq Al-Awsat—One of the four men who carried out a fatal suicide bomb attack on Saudi border guards last Monday recruited some of his family members to join the Islamic State of Iraq and Syria (ISIS), informed sources have told Asharq Al-Awsat.

The sources said Salim Mohammed Al-Shammari, a Saudi national, went to Syria via Turkey during 2013 to fight with ISIS, taking with him some members of his family whom he had persuaded to join the extremist group.

Other members of the family also went to Syria during 2013 in separate groups, the source—who requested anonymity because he is not authorized to brief the media—said.

The source said the four attackers had initially been fighting in Syria but went to Iraq during shortly before the attack.

The four men carried out the attack last Monday on a border patrol near the city of Arar on the Saudi frontier with Iraq’s Anbar province.

During the attack, Shammari’s associates exchanged gunfire with border guards, and Shammari detonated an explosives belt after reinforcements arrived, killing three border guards including commanding officer Gen. Oudah Al-Belawi.

In comments to Asharq Al-Awsat on Saturday, Interior Ministry spokesman Maj. Gen. Mansour Al-Turki said three of the four were Saudi nationals who left the Kingdom separately in 2013. One of them was previously arrested for having ties to Al-Qaeda but was released on bail.

Security forces seized automatic weapons, hand grenades and explosive belts, including more than 100,000 Saudi Riyals, at the scene of the attack.

Saudi Arabia is one of the countries in the US-led international coalition against ISIS, which has carried out airstrikes on the group in Iraq. The group has repeatedly warned it would be carrying out attacks in the Kingdom in reprisal.