The FBI has started investigating Hillary Clinton's controversial use of private email as Secretary of State and has contacted a firm that managed the setup, along with her attorney, The Washington Post reported.
Clinton's electronic correspondence has been under scrutiny since her admission in March that she had used a private account for her email correspondence while secretary of state between 2009 and 2013.
The Justice Department received a referral to probe the storage of the emails last month, after an assessment that her private account contained "hundreds of potentially classified emails."
The FBI inquiry is looking into the servers and other systems Clinton had set up to handle those emails, the Post reported. The FBI is also looking into how the emails in question are currently stored.
"The government is seeking assurance about the storage of those materials. We are actively cooperating," Clinton's lawyer David Kendall told the Post.
Republican rivals contend that Clinton, frontrunner for the Democratic presidential nomination in 2016, used the private account in order to keep it out of the public record.
She says she handled her email this way for the convenience of carrying a single smartphone.
Clinton's campaign meanwhile declined to address the FBI's investigation. Campaign spokesman Nick Merrill said the release of thousands of Clinton's work emails was under way, and should be sped up.
"We want to ensure that appropriate procedures are followed as these emails are reviewed while not unduly delaying the release of her emails," he told the Post.
"We want that to happen as quickly and as transparently as possible."
Republicans in Congress also have been holding Clinton's feet to the fire over her handling of the deadly 2012 attack on the US consulate in Benghazi, Libya which left three Americans dead.
Clinton is scheduled to testify in Congress in October over the Benghazi affair.