Democratic candidate Hillary Clinton said on Friday she was sorry that her use of a personal email account while secretary of state caused confusion, in her most contrite comments yet about an issue that is plaguing her White House bid.

Clinton, the Democratic front-runner ahead of the November 2016 presidential election, did not apologize for her own behavior but said she was wrong not to use a government email account when she was serving as the nation's top diplomat.

"At the end of the day I am sorry that this has been confusing to people and has raised a lot of questions but there are answers to all these questions," she told MSNBC in an interview.

Clinton has faced steady criticism from political opponents since it emerged in March that she used her own email account on an unsecured private server in her New York home for official business, rather than a government-issued email address.

"I certainly wish that I had made a different choice and I know why the American people have questions about it," Clinton said. "I take responsibility. I should have had two accounts, one for personal and one for work-related," she said.

Doubts over Clinton's trustworthiness have damaged her poll numbers, allowing liberal Vermont Senator Bernie Sanders to narrow the gap with her as the first nominating contests for the election approach early next year.

Clinton said that while she should have behaved differently, she had done nothing wrong. "It was allowed and it was fully above board. The people in the government knew that I was using a personal account," she said.

The FBI is now investigating the security of the private server and any classified information on it.