Unknown assailants detonated a bomb outside a Christian school in Gaza City before dawn Friday, causing no injuries. The explosion was heard in surrounding neighborhoods at around 4 a.m. Damage was visible at the entrance to the Zahwa Rosary School, which is run by Catholic nuns but caters mainly to Muslim students. Two nuns were in their convent adjacent to the school when the bomb went off, a school official said, and were shaken but unharmed. The official declined to be named, saying she was frightened by the incident and concerned for her safety. The incident appeared to be the work of a poorly trained individual or group, she said - police told school officials that the bomb had been set incorrectly, and it caused little damage. The bombing was the latest in a string of attacks on Christian institutions in the overwhelmingly Muslim territory. In the most serious attack, a local Christian activist was murdered in October. His killers have not been found. Friday's bombing was not the first attack on the school run by the Rosary Sisters. The school was ransacked in June, 2007, along with the nuns' adjacent convent, during a week of intense fighting that ended with Hamas' seizure of power. Police officials from Hamas said they were looking into the incident. But the school official said the police's inability to find perpetrators of previous attacks was cause for concern. "We don't feel safe. There's no security here," she said. Father Manuel Musallem, the leader of Gaza's Catholics, played down Friday's attack. "This is the work of a dark individual," Musallem said. "We have excellent relations with Muslims. They enter our houses and we enter theirs. There's no campaign of Muslims against Christians here," he said. About 3,200 Christians live in Gaza among 1.4 million Muslims. Relations between Christians and Muslims have traditionally been good, and Christians have held a respected place in Gaza's society as members of the territory's small elite, running schools, hospitals and businesses. But members of the tiny community have grown increasingly uneasy since Hamas routed forces of the secular Fatah movement and became the sole power in the territory.