Twin brothers in Riyadh have stabbed their entire family, killing their mother and seriously injuring their father and elder brother. The 20-year-olds are reportedly loyal to Islamic State (IS, formerly ISIS/ISIL).

The twins, Khalid and Saleh Al Areeni, allegedly carried out the attack in their family home in the Saudi capital on Friday. According to investigators, the young men first stabbed their mother with a cleaver and sharp knives brought from the outside, before going after their father. They then chased their elder brother and stabbed him multiple times as well. Having thought the entire family was finished, the twins fled the scene in a stolen car.

The two stabbed men were critically injured and taken to hospital, while the woman died on the spot. Hundreds turned up at the slain mother’s funeral this weekend, Gulf News reported, adding that people prayed for her as they would for a terror victim.

After a large-scale manhunt, police caught the brothers some 100km (62 miles) from the capital. According to a statement issued by the Saudi interior ministry, the crime was premeditated and the twins were found to be loyal to IS.

According to local reports, the attackers decided to kill their mother after she found out about their plans to join IS. Apparently, the woman told her sons that she would report them to authorities if they kept planning to leave the country to join IS in combat zones.

Earlier in June, citing intelligence data, the US State Department announced that more than 40,000 foreign militants from 100 countries had been fighting in Syria as IS mercenaries. Russia has previously released similar warnings, saying that up to 30,000 foreigners have joined the ranks of the terrorist group. Both nations have been fighting Islamic extremists in the Middle East, with Saudi Arabia also being part of the US-led coalition aimed at eradicating IS.