Militants killed at least three people Monday and wounded 17 when they fired on a bus carrying workers in the North Sinai town of Al-Arish, security and medical sources said. 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 bus was attacked with a rocket-propelled grenade near Al-Arish airport. Three people died and 17 were injured in the attack,\" a security official said. A medical source confirmed the toll, adding that \"many of those injuries are critical.\" The bus was carrying workers from a cement factory. The 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. The restive Sinai peninsula has been hit by a surge of violence since president Mohamed Morsi\'s ouster on July 3, with militants killing a police officer early on Friday. A Coptic Christian man found decapitated a day earlier, while two people died in an attack on a checkpoint in the peninsula on Wednesday.