Jimmy Lai, a Hong Kong media mogul and one of the city's most prominent pro-democracy figures, was arrested on Monday under Beijing's new national security law, a close aide and a police source said. "Jimmy Lai is being arrested for collusion with foreign powers at this time," Mark Simon, a colleague of Lai's, wrote on Twitter. A police source told AFP Lai was arrested on charges of colluding with foreign forces -- one of the new national security offences -- and with fraud. jta/axn