In an interview with ABC News, Sen. Elizabeth Warren, D-Mass., insisted she is not seeking a presidential bid despite suggestions that she could present a formidable threat to former Secretary of State Hillary Clinton in 2016.

"I'm not running for president," Warren told ABC News' David Muir in an interview at her home in Cambridge, Mass.

Asked about a recent story that suggested she is "Hillary's nightmare," Warren said, "I don't get who writes these headlines or what they're about. I think there's just kind of a pundit world out there."

"Do you think Hillary Clinton would make a good president?" Muir asked.

"I think Hillary Clinton is terrific," Warren said. "We gotta stay focused on these issues right now."

Watch the full interview with Sen. Elizabeth Warren TONIGHT on "World News with Diane Sawyer."

Though she did not directly answer whether Clinton would make a good president, Warren was one of 16 Democratic female senators who signed a secret letter to Clinton last year urging her to run for president in 2016.

Warren's rejection of a presidential run come ahead of the release of her new book, "A Fighting Chance ," which has already prompted speculation about her ambitions.

Warren, a former Harvard law professor, won her Massachusetts Senate seat in 2012, and her message of economic populism has resonated among Democrats nationwide. The popularity has spurred some progressive candidates running in the 2014 mid-term elections to dub themselves as part of the "Elizabeth Warren wing of the Democratic Party."

Warren's new book details her vision for helping the middle class while also recounting her upbringing in a middle-class household. " A Fighting Chance" will be released Tuesday, April 22.