An explosion believed to have been caused by a bomb ripped through the military intelligence building in Libya's eastern city of Benghazi, causing damage to the structure and nearby homes but no injuries, a security official said."The department of military intelligence was bombed," a senior security officer told the AFP news agency on Wednesday, adding that the level of damage to the two-storey building suggested it was hit by an improvised explosive device.The dawn blast punched out large holes in the exterior walls of the building, marking the second attack on the facility in as many months. Adjacent buildings were also touched."The incident did not result in injury to any of the guards of the residents of neighbouring buildings," said the official who did not wish to be named.The identity of the attackers, he said, remains unknown."The blast happened right after the al-fajr [dawn] prayers, the people who witnessed the explosion said that a man carrying a sack got out of a silver car with a damaged door, then the car went around the building and then the explosion happened as you see," said Hussein Al-Baraasi, who spoke to the Reuters news agency at the scene.Adil Othmane, an army spokesperson in Tripoli, confirmed the incident and said it was under investigation. He attributed the attack to the absence of security guards.Khaled Haidar, spokesperson for the director of national security in Benghazi, said the eastern city has witnessed a series of security breaches over the past week.These included the discovery and neutralisation of a bomb outside the iconic Tibesti Hotel on Sunday.On Friday, saw a hand grenade hit the appeals court and a rocket punch the outside wall of the main prison. Both incidents caused only minor material damage to the buildings targeted, he said.Also on Friday, Haidar added, security forces diffused two time-bombs planted by the office of national security in Benghazi.