Hillary Clinton, the Democratic front-runner for the 2016 US presidential election, did not apologize for her behavior but said she was wrong not to use a government email account when she became America's top diplomat in 2009.

"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 NBC News in an interview on Friday.

The former secretary of state acknowledged she did not "stop and think" about her email set-up when she took office. "There was so much work to be done. We had so many problems around the world," she said. Clinton stated that she took responsibility for the decision to use a private email account and server based at her home in suburban New York.

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

In August, Clinton handed her private server over to the FBI.

In the NBC interview, she reiterated that she did not "send or receive any material marked as classified," underlining that she dealt with such material "in person."

das/cmk (AP, Reuters)