Hillary Clinton and Barack Obama are both fighting reports that their campaigns are in talks about Clinton possibly cutting her losses and joining up as Obama's running mate.

Clinton called such reports "flatly untrue," in an interview Friday with the Sioux Falls Argus Leader editorial board, adding that she is not planning any such discussions.

Asked if her campaign had any discussions with the Obama campaign about her possibly bowing out in exchange for the vice president slot, Clinton said: "It is flatly untrue and it is not anything I'm entertaining. It is nothing I have planned and it is nothing I am prepared to engage in. I am still vigorously campaigning."

Obama spokesman Robert Gibbs also said such speculation is "completely untrue."

"Both campaigns I think are rightly focused on the last three contests that are left in the race and after that we'll know the nominee," he told FOX News. "There haven't been any discussions with the Clinton campaign on this topic."

Meanwhile, Sen. Dianne Feinstein, D-Calif., a staunch Clinton supporter, said Friday she believes that if Obama becomes the nominee he should select Clinton as his running mate.

"I think as this race has emerged each one of them has garnered a different constituency and different states, and therefore when you put the two of them together it forms, I believe, the strongest ticket," she told The Associated Press in a phone interview.

Former Fannie Mae CEO Jim Johnson is overseeing the early vetting of possible vice presidential running mates for Obama, Democratic officials say. He did the same job for Democratic nominees John Kerry in 2004 and Walter Mondale in 1984.

But in her editorial board interview, Clinton tried to muffle calls for the Democratic race to end.

"Between my opponent and his camp and some in the media there has been this urgency to end this, and you know historically that makes no sense. So I find it a bit of a mystery," she said.

Clinton continued to argue that she has a popular-vote advantage and that the dispute over the Michigan and Florida primaries still must be resolved.

Clinton won those contests, but the states were stripped of their delegates for holding early primaries.

FOX News' Major Garrett and The Associated Press contributed to this report.