CAIRO, May 16 (Aswat Masriya) - Gunmen opened fire on a vehicle in North Sinai's al-Arish city leaving three prosecutors and a driver dead on Saturday, Egypt's state television reported. 

The attack also left a prosecutor injured. The vehicle was on its way to court when the attack occurred.  

Police sources said the attack was carried out by militants belonging to the Sinai-based militant group Ansar Bayt al-Maqdis.

The sources believe the attack came in response to a court decision earlier today to refer ousted Islamist President Mohamed Mursi to the Grand Mufti, a step that must be taken in Egypt's court system ahead of issuing a death sentence. 

Egypt's top prosecutor Hisham Barakat ordered an immediate investigation, tasking prosecutors with inspecting the scene.    

President Abdel Fattah al-Sisi ordered providing judges with the necessary protection, especially those working in areas suffering from "violence and terrorism", a statement from his office read. 

Ansar is Egypt's most notorious militant group and has claimed more responsibility for militant attacks across Egypt than any other group.

It changed its name to Sinai Province after pledging allegiance to the leader of the Islamic State fighters, last year. 

Most of the group's attacks are carried out in the north of the Sinai peninsula.