Hillary Clinton said she wouldn't rule out challenging the legitimacy of the 2016 presidential election if Russian interference turned out to be deeper than previously thought.

"No, I wouldn't rule it out," she said in an interview with NPR published Monday.

The defeated Democratic nominee stressed, however, that she does not believe there is a means to officially challenge the election's outcome.

"I don't know if there's any legal, constitutional way to do that," Clinton said. "I think you can raise questions."

Clinton has repeatedly blamed Russia's efforts to intervene in last year's election for her loss to Donald Trump, but her latest comments reflect the depth of her frustration with the Kremlin's efforts.

They come as special counsel Robert Mueller is investigating the election-meddling campaign that U.S intelligence agencies say was done to benefit Trump, and whether any of the president's associates colluded with Moscow.

"[Trump] knew they were trying to do whatever they could to discredit me with emails, so there's obviously a trail there," Clinton said. "I don't know that in our system we have any means of doing that, but I just wanted to add to the point you made. There's no doubt they influenced the election: We now know more about how they did that."

The president has questioned the intelligence community's conclusion that Russia was behind the election interference campaign, and Mueller is reportedly probing whether Trump's firing of FBI Director James Comey was an attempt to obstruct the investigations.

Clinton said she would have reacted differently than Trump did and established an "independent commission with subpoena power" to probe it.

"Let me just put it this way, if I had lost the popular vote but won the electoral college and in my first day as president the intelligence community came to me and said, 'The Russians influenced the election,' I would've never stood for it," she said. "Even though it might've advantaged me, I would've said, 'We've got to get to the bottom of this.'"