The FBI is trying to determine whether as many as five Americans were part of a team of terrorists who took over a Kenyan mall over the weekend, unleashing an attack that led to the death of at least 68 people, NBC News reports.

The probe comes after a group purporting to be behind the attacks, Somali al-Qaeda affiliate al-Shabab, indicated Americans were involved and listed their names and home states.

At least two of them came from the St. Paul-Minneapolis area in Minnesota, which has a large Somali population, the group claimed, according to NBC News.