Unidentified attackers have killed at least three people and wounded 17 others in the restive Egyptian region of North Sinai, security and medical sources have said. The attackers reportedly fired rocket propelled grenades at a bus carrying cement factory workers in the city of al-Arish, causing the vehicle to turn over and collide with an oncoming truck. The injured were taken to al-Arish hospital, and many were reported to be in critical condition. According to witnesses, the bus was driving near an armoured vehicle that was the real target of the grenades. Military spokesman Colonel Ahmed Aly said in a statement that a \"terrorist group\" had been targeting a police vehicle but hit the workers\' bus by mistake. The Sinai Peninsula, bordering Israel and the besieged Gaza Strip, has been hit by a surge of violence since president Mohammed Morsi’s oust on July 3, with fighters killing a police officer early on Friday. A Coptic Christian man was found decapitated a day earlier, while two people died in an attack on a checkpoint in the peninsula on Wednesday. Monday’s attack came hours after gunmen clashed with the Egyptian army near the Israeli border. The fighting broke out in the area of al-Wifaq, in Northern Sinai, after militants tried unsuccessfully to blow up a police vehicle with explosives.