Hillary Clinton addressing her staff and supporters about the results of the US election at a hotel in New York. Thomson Reuters Former Democratic presidential nominee Hillary Clinton on Thursday made her first public statements about Russia's cyberattacks on Democrats during the US election, saying Russian President Vladimir Putin attempted to "undermine our democracy" because of his "personal beef" with her.

"We're learning more every day about the Russians' unprecedented plot to swing the election," she told a group of campaign donors at Manhattan's Plaza Hotel on Thursday night, according to audio obtained by The New York Times.

"Putin personally directed these attacks ... apparently because he has a personal beef against me," Clinton said. "He is determined not only to score a point against me, which he did, but also to undermine our democracy ... It's part of a long-term [Russian] strategy to cause us to doubt ourselves."

Tension between Clinton and Putin goes back to at least 2011, when, as secretary of state, Clinton suggested that Russia's parliamentary elections were not free or fair. Putin perceived her comments as meddling and blamed her for the protests that broke out in Russia afterward.

"Putin publicly blamed me for the outpouring of outrage by his own people, and that is the direct line between what he said back then and what he did in this election," Clinton told donors on Thursday, reiterating her obligation to denounce elections that were "so flawed, so illegitimate, that it was embarrassing."

"Make no mistake," she said, pivoting back to the Russian hacking campaign. "This is not just an attack against me and my campaign, although that may have added fuel to it. This is an attack against our country. We are well beyond normal political concerns here. This is about the integrity of our democracy and the security of our nation."

During an interview with NPR on Thursday, President Barack Obama promised retaliatory action against Russia. The CIA has concluded that Russia intervened in the US election to try to tip the scales toward President-elect Donald Trump. Other agencies haven't gone as far in their assessments regarding the motive, but US intelligence agencies publicly accused Russia of interference in October.

FBI Director James Comey testifying before the House Judiciary Committee on September 28 in Washington, DC. Comey testified on a variety of subjects including the investigation into Clinton's email server. Getty/Winn McNamee

Clinton also attributed her loss to Trump to the bombshell letter released by FBI Director James Comey just over one week before Election Day. The letter informed members of Congress about new emails related to the investigation into her private email server.

"There were some events, some unprecedented factors, that I don't think we can ignore because to do so is at our peril," she said. "Swing-state voters made their decisions in the final days breaking against me because of the FBI letter from Director Comey."

Two days before the election, after agents examined the newly discovered emails, Comey announced that the agency would not change its initial recommendation not to indict Clinton for her use of the private server.

"That letter most likely made the difference in the outcome," she said, echoing a letter sent out by the campaign's director of opinion research, Navin Nayak, days after the election.

"We believe that we lost this election in the last week. Comey's letter in the last 11 days of the election both helped depress our turnout and also drove away some of our critical support among college-educated white voters — particularly in the suburbs," Nayak wrote. "We also think Comey's 2nd letter, which was intended to absolve Sec. Clinton, actually helped to bolster Trump's turnout."

Listen to Clinton's remarks here: