ISIS launched attacks in their stronghold around the city of Rafah in response to the kidnapping of three ISIS fighters by local tribes.

Three people were injured in clashes between militants and local tribes in the Sinai peninsula in a fight that began when militants shot at a truck smuggling cigarettes, Egyptian security officials said Monday.

The officials told The Associated Press that ISIS group militants launched RPG attacks on Sunday in their stronghold around the city of Rafah in response to the kidnapping of three ISIS fighters by local tribes.

The unrest started when militants shot at a truck smuggling cigarettes into the area, where the ISIS imposes a strict version of Islamic law that prohibits the sale of tobacco, tribal sources said.

The government officials spoke on condition of anonymity as they were not authorized to brief the media. The tribal sources requested anonymity for fear of reprisal.

The incident marks an escalation in tension between the two sides over the imposition of Islamic Law in northern Sinai.

Last month, female teachers commuting from the region’s urban center, El-Arish, to Rafah reported being stopped by militants twice in one week and were asked not to take the road without a male relative in compliance with Islamic law. Locals said the militants had previously intercepted trucks carrying cigarettes and punished passengers with flogging.

Northern Sinai residents have been caught in a violent battle between militant groups who have expanded their activity in the Peninsula since the removal of Islamist President Mohammed Morsi in 2013 and security forces waging war against them.

Militants have beheaded locals accused of collaboration with authorities and recently stepped up their attacks against the peninsula’s Coptic Christian minority, forcing hundreds to flee following a string of killings in the city of Arish in February.