(Reuters) – An 18-year-old man was arrested in New Jersey on Thursday on a charge of threatening to attack Jewish people, which had prompted the FBI last week to issue an unusual warning to synagogues across the state to bolster security. Omar Alkattoul of Sayreville, New Jersey, is due to make his first appearance in U.S. District Court on Thursday afternoon to face one count of transmitting an online threat to injure others. On Nov. 1, Alkattoul is accused of using a social media application on his phone to send another person a document he had written about attacking Jews called “When Sword…