On Wednesday, in the deadliest attack in Northern Africa since 2002, two gunmen dressed in military-style clothing burst from a vehicle in the capital city of Tunis at the National Bardo Museum and opened fire, gunning down tourists and civilians.

The two men, identified as Yassine Laabidi and Hatem Khachnaoui, proceeded to enter the museum, taking hostages, before they were killed by security forces. Habib Essidi, Tunisia’s prime minister, said that Laabidi had been previously flagged by intelligence for nothing “special”, but no formal links had been established between any terror groups.

ISIS was not previously thought to have had a foothold in Tunisia, but is present in neighboring Libya and Algeria, and some are speculating that the attack that left at least 19 dead and 44 injured in Tunis might be linked to the death of a senior ISIS commander, Ahmed Rouissi, whose body was found last week near the city of Sirte. Rouissi was a leading member of Tunisia’s Ansar al-Sharia terror group, and is believed to be responsible for the killing of two Tunisian opposition leaders in 2013.

The attack seems to have been planned at least a week in advance because, after scouring Twitter, the Muslims in the area were warned to stay away from “infidel sites” -code for tourists sites like the museum- in the time surrounding the attack.

Twitter accounts associated with ISIS terror group were overjoyed, and urged Tunisians to “follow their brothers,” according to the Rita Katz of SITE, a U.S.-based organization that monitors militant groups.