Three blasts ripped through a courthouse in the eastern city of Benghazi on Friday causing serious damage to the building but no casualties, Libyan security sources said. One of the explosions punched a hole three metres (10 feet) in diameter through the walls of the courthouse on Meidan al-Shajara, a public square flanked by several government offices and the National Oil Corporation, an AFP journalist said. Libyan state news agency Lana said three devices went off early Friday. Three people were wounded and damage was caused to the building\'s fence and surrounding structures. Security sources told AFP that \"unknown assailants booby-trapped the building\" and set off the explosion at \"exactly 5 am (0300 GMT).\" Security official Aghdour bin Zablah however said the explosives were thrown out of a passing car. The area was cordoned off, the journalist said. Witnesses and residents told AFP the blast was very intense. \"It left residents in the area and patients being treated in a nearby hospital completely shaken up,\" one said. Late Thursday, clashes sparked by a prison revolt in Benghazi, cradle of the revolt that toppled Muammar Gaddafi\'s regime last year, left one person dead and at least four wounded. The Mediterranean city has been hit by sporadic acts of violence this year, including an attack on government buildings, the desecration of a World War II cemetery, clashes at political rallies and a failed bombing of a UN convoy.