Three explosions rocked Gaza City early Sunday, damaging two Internet cafes and a Christian bookstore. No one was hurt and no group claimed responsibility for the blasts, which took place around 3 a.m. local time, Palestinian security officials said. Several similar attacks on Internet cafes and music stores in recent months have been claimed by a little-known extremist Islamic organization calling itself the "Swords of Truth." The officials would not speculate on the identity of the attackers behind the Sunday attacks, saying only that the incidents were under investigation. The officials spoke on condition of anonymity because they were not authorized to speak to the press. Heavy external damage was visible at the three stores. At the bookstore, which is funded by American Protestants and known as the Bible Society, a number of books were also burned in the explosion. In recent months, about three dozen Internet cafes and shops selling pop music have been attacked in the Gaza Strip, with assailants detonating small bombs outside businesses at night, causing damage but no injuries. Palestinian security officials have said they suspect a secret "vice squad" of Muslim militants.