Warsaw - US President Barack Obama on Saturday ducked questions about an FBI investigation into Hillary Clinton's use of a private email account for sensitive government business.After months of refusing to comment on the ongoing legal probe, with that investigation now completed, Obama said he would "continue to be scrupulous about not commenting on it". Obama has backed Clinton's bid to replace him as president after elections this November.She is expected to be formally nominated as the Democratic presidential nominee later this month.The FBI has been scathing in its criticism of Clinton, even though it decided not to pursue criminal charges.FBI director James Comey found Clinton, while careless, did not break the law.Republicans have called for Clinton to be prosecuted and for her customary intelligence briefings to stop.Obama did say that he shared Comey's concerns about the treatment of classified mail at the State Department, which Clinton once run."I am concerned," he said. "The challenge that we've got is primarily driven by the changing nature of how information flows. The advent of email and texts and smartphones is just generating enormous amount of data.""It is hugely convenient," he said, but it adds "enormous pressure on the department to sort through it, classify it properly".