Unidentified gunmen stopped a bus transporting police officers and shot four of them dead Saturday night in Egypt’s restive Sinai Peninsula, bringing the day’s death toll to six after an early morning attack targeting a police officer killed two bystanders.

The assailants then fled into the desert in a 4×4 truck. Nearby in Al-Arish, where a wall was recently built around the city to keep out militants, a shootout took place between gunmen and security forces on its western border. No casualties were sustained.

Saturday night’s attack was eerily similar to a 19 August 2013 incident during which militants stopped a number of buses transporting police conscripts and executed 25 of them in the Sinai’s Rafah. The attack was allegedly staged in response to the violent dispersal of pro-Morsi sit-ins in Cairo and Giza.

Attacks against security forces have skyrocketed since Mohamed Morsi’s ouster. Ansar Beit Al-Maqdis, an Al-Qaeda inspired militant organization based in the Sinai, has claimed the majority of violent attacks against both police and army forces.

No group has claimed responsibility for Saturday’s shootings.