WASHINGTON • Mrs Hillary Clinton has apologised for using a private e-mail server while she was US secretary of state, calling the decision, which has dogged her bid for the Democratic presidential nomination, a "mistake".

The Democratic front runner, who is facing eroding support, has long dismissed the e-mail uproar as a manufactured imbroglio.

But in an interview with ABC's World News Tonight, she said she took full responsibility for the episode, which she regretted.

"That was a mistake. I'm sorry about that. I take responsibility," she told the news network on Tuesday evening.

Mrs Clinton used her private e-mail account and home server in lieu of the official government e-mail system while she served as top diplomat from 2009 to 2013.

Until Tuesday, she had demurred from issuing a direct apology. "I certainly wish that I had made a different choice," Mrs Clinton said last week, adding that she was "sorry" the controversy was "confusing" for the public.

"As I look back at it now, even though it was allowed, I should have used two accounts, one for personal e-mails, one for work-related e-mails," she said during Tuesday's interview.

The lingering e-mail saga has weighed on Mrs Clinton's popularity, with a Gallup poll released last Friday showing her favourability rating at 41 per cent, compared with 51 per cent who view her unfavourably - the lowest level since 1992.

But the former first lady maintained she could weather the storm, telling ABC: "I can survive it, because I think I'm running to be president to do what the country needs done."

However, the issue is unlikely to go away soon, since the State Department, to which Mrs Clinton turned over 30,000 official e-mail messages late last year, is publicly releasing them in batches. She has also turned over the home server.

Many contain information that has been retroactively classified, raising questions about whether Mrs Clinton was inappropriately sending and receiving highly sensitive material, and whether there were enough security measures to protect her server from hackers.

Mrs Clinton maintained that during her tenure at the State Department, she "did not send or receive any information that was marked classified at the time".

She also added that "everyone" she had e-mailed with, including "people in the White House, of course across the State Department", knew that she was using a personal account. "It appeared, you know, as my address."

The Federal Bureau of Investigation is examining the server to determine whether the arrangement has compromised government secrets.

AGENCE FRANCE-PRESSE