Mon Sep 23, 2013 AT 6:00 AM EDT
Al-Shabaab, an Islamic terrorist group linked to al-Qaeda, killed at least 68 people in an attack on a mall in Kenya this weekend, reports the BBC. The group’s Twitter post claimed three of the attackers were from the United States, and NBC reports the FBI is investigating whether as many as five of the attackers were Americans. ABC reports that the group has recruited dozens of Americans to join its cause over the past six years.