The FBI has launched an investigation into the security of the private email server that Hillary Clinton used when she was secretary of state.
"We are actively cooperating" with the investigation, lawyer David Kendall said in a statement.
Mrs Clinton’s emails have been under scrutiny since it was revealed she used a private server in her Chappaqua, New York, home while she was the top US diplomat.
As the campaign for next year’s presidential election has gathered pace and opponents have sought to put pressure on Ms Clinton, government and congressional investigators have been trying to determine whether she sent or received classified information on unsecured email.
According to a report in the Washington Post, the FBI has also asked Mr Kendall, about the security of a thumb drive, containing copies of the Democrat’s emails, that the lawyer possesses.
The Associated Press said that last month, the inspector general of the US intelligence community alerted the Justice Department about classified information that was improperly included on email correspondence that went through Mrs Clinton's home server.
The referral to the Justice Department did not seek a criminal probe and did not specifically target Mrs Clinton. Officials have said the FBI is not investigating her but only the security of her server.
A spokesman for Mrs Clinton’s presidential campaign, Brian Fallon, tweeted said in message on social media that the report in the Post story did not “change anything”.
“IG request was noncriminal & didn't accuse Clinton of wrongdoing,” he said. “FBI is not targeting her.”
The FBI has yet to comment on the report. But opponents of Mrs Clinton have seized on the incident, saying it underscores public distrust of Mrs Clinton and a view that she thinks that normal rules do not apply to her.Reuse content